diff --git a/app/Http/Controllers/Api/CashflowAnalyticsController.php b/app/Http/Controllers/Api/CashflowAnalyticsController.php
index c4edd40a..906f25ed 100644
--- a/app/Http/Controllers/Api/CashflowAnalyticsController.php
+++ b/app/Http/Controllers/Api/CashflowAnalyticsController.php
@@ -7,9 +7,11 @@ use App\Enums\CategoryType;
 use App\Http\Controllers\Controller;
 use App\Models\Category;
 use App\Models\Transaction;
+use App\Models\User;
 use App\Services\CategoryTree;
 use App\Services\ExchangeRateService;
 use App\Services\PeriodComparator;
+use App\Services\UserMonthPeriodService;
 use Carbon\Carbon;
 use Illuminate\Http\JsonResponse;
 use Illuminate\Http\Request;
@@ -20,6 +22,7 @@ class CashflowAnalyticsController extends Controller
     public function __construct(
         private ExchangeRateService $exchangeRateService,
         private CategoryTree $tree,
+        private UserMonthPeriodService $userMonthPeriodService,
     ) {}
 
     public function summary(Request $request): JsonResponse
@@ -78,17 +81,19 @@ class CashflowAnalyticsController extends Controller
         $user = $request->user();
 
         if (isset($validated['from'], $validated['to'])) {
-            $start = Carbon::parse($validated['from'])->startOfMonth();
-            $end = Carbon::parse($validated['to'])->endOfMonth();
+            $start = Carbon::parse($validated['from'])->startOfDay();
+            $end = Carbon::parse($validated['to'])->startOfDay();
         } else {
             $months = $validated['months'] ?? 12;
-            $end = isset($validated['to'])
-                ? Carbon::parse($validated['to'])->endOfMonth()
-                : Carbon::now()->endOfMonth();
-            $start = $end->copy()->subMonthsNoOverflow($months - 1)->startOfMonth();
+            $endPeriod = $this->userMonthPeriodService->monthContaining(
+                $user,
+                isset($validated['to']) ? Carbon::parse($validated['to']) : Carbon::now(),
+            );
+            $end = $endPeriod['end_inclusive'];
+            $start = $endPeriod['from']->copy()->subMonthsNoOverflow($months - 1);
         }
 
-        $monthlyTotals = $this->getMonthlyTrendTotals($user->id, $user->currency_code, $start, $end);
+        $monthlyTotals = $this->getMonthlyTrendTotals($user->id, $user->currency_code, $start, $end, $user);
 
         $data = [];
         $current = $start->copy();
@@ -326,7 +331,7 @@ class CashflowAnalyticsController extends Controller
         return $categorized;
     }
 
-    private function getMonthlyTrendTotals(string $userId, string $userCurrency, Carbon $from, Carbon $to): Collection
+    private function getMonthlyTrendTotals(string $userId, string $userCurrency, Carbon $from, Carbon $to, User $user): Collection
     {
         $transactions = Transaction::query()
             ->where('transactions.user_id', $userId)
@@ -337,7 +342,9 @@ class CashflowAnalyticsController extends Controller
         $this->preloadExchangeRates($transactions, $userCurrency);
 
         return $transactions
-            ->groupBy(fn (Transaction $transaction): string => $transaction->transaction_date->format('Y-m'))
+            ->groupBy(fn (Transaction $transaction): string => $this->userMonthPeriodService
+                ->monthContaining($user, $transaction->transaction_date)['from']
+                ->format('Y-m'))
             ->map(function (Collection $transactions) use ($userCurrency): array {
                 $income = 0;
                 $expense = 0;
diff --git a/app/Http/Controllers/DashboardController.php b/app/Http/Controllers/DashboardController.php
index 546e3603..ca5cdd10 100644
--- a/app/Http/Controllers/DashboardController.php
+++ b/app/Http/Controllers/DashboardController.php
@@ -8,6 +8,7 @@ use App\Models\Transaction;
 use App\Services\AccountMetricsService;
 use App\Services\CategoryTree;
 use App\Services\PeriodComparator;
+use App\Services\UserMonthPeriodService;
 use Carbon\Carbon;
 use Illuminate\Http\Request;
 use Illuminate\Support\Collection;
@@ -20,6 +21,7 @@ class DashboardController extends Controller
     public function __construct(
         private AccountMetricsService $accountMetricsService,
         private CategoryTree $tree,
+        private UserMonthPeriodService $userMonthPeriodService,
     ) {}
 
     public function __invoke(Request $request): Response
@@ -50,11 +52,9 @@ class DashboardController extends Controller
     private function getTopCategories(Request $request): array
     {
         $user = $request->user();
-        $now = Carbon::now();
-        $from = $now->copy()->subDays(30);
-        $to = $now->copy();
+        $periodDates = $this->userMonthPeriodService->current($user);
 
-        $period = new PeriodComparator($from, $to);
+        $period = new PeriodComparator($periodDates['from'], $periodDates['end_inclusive']);
         $previousPeriod = $period->previous();
 
         $currentSpending = $this->getCategorySpending($user->id, $period->from, $period->to);
@@ -85,11 +85,9 @@ class DashboardController extends Controller
     private function getCashflowSummary(Request $request): array
     {
         $user = $request->user();
-        $now = Carbon::now();
-        $from = $now->copy()->startOfMonth();
-        $to = $now->copy()->endOfMonth();
+        $periodDates = $this->userMonthPeriodService->current($user);
 
-        $period = new PeriodComparator($from, $to);
+        $period = new PeriodComparator($periodDates['from'], $periodDates['end_inclusive']);
         $previousPeriod = $period->previous();
 
         return [
diff --git a/app/Http/Requests/Settings/ProfileUpdateRequest.php b/app/Http/Requests/Settings/ProfileUpdateRequest.php
index 962e9803..4d30e587 100644
--- a/app/Http/Requests/Settings/ProfileUpdateRequest.php
+++ b/app/Http/Requests/Settings/ProfileUpdateRequest.php
@@ -4,6 +4,7 @@ namespace App\Http\Requests\Settings;
 
 use App\Models\User;
 use App\Services\CurrencyOptions;
+use App\Services\UserMonthPeriodService;
 use Illuminate\Contracts\Validation\ValidationRule;
 use Illuminate\Foundation\Http\FormRequest;
 use Illuminate\Validation\Rule;
@@ -32,6 +33,7 @@ class ProfileUpdateRequest extends FormRequest
             ],
             'currency_code' => ['required', 'string', 'max:3', Rule::in($currencyOptions->primaryCodes())],
             'locale' => ['nullable', 'string', Rule::in(['en', 'es'])],
+            'month_start_day' => ['required', 'integer', Rule::in(UserMonthPeriodService::ALLOWED_START_DAYS)],
         ];
     }
 }
diff --git a/app/Models/User.php b/app/Models/User.php
index 5ccb5784..33e26274 100644
--- a/app/Models/User.php
+++ b/app/Models/User.php
@@ -47,6 +47,7 @@ class User extends Authenticatable implements HasLocalePreference, MustVerifyEma
         'currency_code',
         'locale',
         'timezone',
+        'month_start_day',
     ];
 
     /**
@@ -76,6 +77,7 @@ class User extends Authenticatable implements HasLocalePreference, MustVerifyEma
             'paywall_seen_at' => 'datetime',
             'last_logged_in_at' => 'datetime',
             'last_active_at' => 'datetime',
+            'month_start_day' => 'integer',
         ];
     }
 
diff --git a/app/Services/UserMonthPeriodService.php b/app/Services/UserMonthPeriodService.php
new file mode 100644
index 00000000..90581a50
--- /dev/null
+++ b/app/Services/UserMonthPeriodService.php
@@ -0,0 +1,54 @@
+<?php
+
+namespace App\Services;
+
+use App\Models\User;
+use Carbon\Carbon;
+use Carbon\CarbonInterface;
+
+class UserMonthPeriodService
+{
+    /** @var list<int> */
+    public const ALLOWED_START_DAYS = [1, 25, 26, 27, 28];
+
+    public function startDay(User $user): int
+    {
+        $startDay = (int) ($user->month_start_day ?? 1);
+
+        return in_array($startDay, self::ALLOWED_START_DAYS, true) ? $startDay : 1;
+    }
+
+    /**
+     * @return array{from: Carbon, to: Carbon, end_inclusive: Carbon}
+     */
+    public function current(User $user, ?CarbonInterface $date = null): array
+    {
+        return $this->monthContaining($user, $date ?? Carbon::now());
+    }
+
+    /**
+     * @return array{from: Carbon, to: Carbon, end_inclusive: Carbon}
+     */
+    public function monthContaining(User $user, CarbonInterface $date): array
+    {
+        $start = $this->monthStartOnOrBefore(Carbon::instance($date->toDateTime()), $this->startDay($user));
+        $to = $start->copy()->addMonthNoOverflow();
+
+        return [
+            'from' => $start,
+            'to' => $to,
+            'end_inclusive' => $to->copy()->subDay(),
+        ];
+    }
+
+    private function monthStartOnOrBefore(Carbon $date, int $startDay): Carbon
+    {
+        $start = $date->copy()->startOfDay()->day($startDay);
+
+        if ($start->gt($date)) {
+            $start->subMonthNoOverflow();
+        }
+
+        return $start;
+    }
+}
diff --git a/database/factories/UserFactory.php b/database/factories/UserFactory.php
index 3a6a4e3f..bb598145 100644
--- a/database/factories/UserFactory.php
+++ b/database/factories/UserFactory.php
@@ -27,6 +27,7 @@ class UserFactory extends Factory
             'name' => fake()->name(),
             'email' => fake()->unique()->safeEmail(),
             'currency_code' => 'USD',
+            'month_start_day' => 1,
             'email_verified_at' => now(),
             'password' => static::$password ??= 'password',
             'remember_token' => Str::random(10),
diff --git a/database/migrations/2026_05_27_120000_add_month_start_day_to_users_table.php b/database/migrations/2026_05_27_120000_add_month_start_day_to_users_table.php
new file mode 100644
index 00000000..ea8aa6a1
--- /dev/null
+++ b/database/migrations/2026_05_27_120000_add_month_start_day_to_users_table.php
@@ -0,0 +1,22 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::table('users', function (Blueprint $table) {
+            $table->unsignedTinyInteger('month_start_day')->default(1)->after('timezone');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('users', function (Blueprint $table) {
+            $table->dropColumn('month_start_day');
+        });
+    }
+};
diff --git a/resources/js/components/cashflow/period-navigation.test.tsx b/resources/js/components/cashflow/period-navigation.test.tsx
index 65d5092a..84ad8b42 100644
--- a/resources/js/components/cashflow/period-navigation.test.tsx
+++ b/resources/js/components/cashflow/period-navigation.test.tsx
@@ -23,6 +23,7 @@ describe('PeriodNavigation', () => {
             <PeriodNavigation
                 currentDate={new Date(2026, 0, 1)}
                 periodType="month"
+                monthStartDay={1}
                 onDateChange={() => undefined}
                 onPeriodTypeChange={() => undefined}
             />,
diff --git a/resources/js/components/cashflow/period-navigation.tsx b/resources/js/components/cashflow/period-navigation.tsx
index 1567dc0d..5c08e632 100644
--- a/resources/js/components/cashflow/period-navigation.tsx
+++ b/resources/js/components/cashflow/period-navigation.tsx
@@ -2,29 +2,22 @@ import { Button } from '@/components/ui/button';
 import { ButtonGroup } from '@/components/ui/button-group';
 import { CashflowPeriodType } from '@/hooks/use-cashflow-data';
 import { useLocale } from '@/hooks/use-locale';
+import {
+    getUserPeriodRange,
+    sameUserPeriod,
+    shiftUserPeriod,
+    UserMonthStartDay,
+} from '@/lib/user-periods';
 import { cn } from '@/lib/utils';
 import { formatDate, formatMonthYear } from '@/utils/date';
 import { __ } from '@/utils/i18n';
-import {
-    addMonths,
-    addQuarters,
-    addYears,
-    getQuarter,
-    isSameMonth,
-    isSameQuarter,
-    isSameYear,
-    startOfMonth,
-    startOfQuarter,
-    startOfYear,
-    subMonths,
-    subQuarters,
-    subYears,
-} from 'date-fns';
+import { getQuarter } from 'date-fns';
 import { ChevronLeft, ChevronRight } from 'lucide-react';
 
 interface PeriodNavigationProps {
     currentDate: Date;
     periodType: CashflowPeriodType;
+    monthStartDay: UserMonthStartDay;
     onDateChange: (date: Date) => void;
     onPeriodTypeChange: (periodType: CashflowPeriodType) => void;
 }
@@ -41,19 +34,34 @@ const periodTypeOptions: Array<{
 export function PeriodNavigation({
     currentDate,
     periodType,
+    monthStartDay,
     onDateChange,
     onPeriodTypeChange,
 }: PeriodNavigationProps) {
     const locale = useLocale();
     const now = new Date();
-    const isCurrentPeriod = samePeriod(currentDate, now, periodType);
+    const periodStart = getUserPeriodRange(
+        currentDate,
+        periodType,
+        monthStartDay,
+    ).from;
+    const isCurrentPeriod = sameUserPeriod(
+        currentDate,
+        now,
+        periodType,
+        monthStartDay,
+    );
 
     const handlePreviousPeriod = () => {
-        onDateChange(shiftPeriod(currentDate, periodType, -1));
+        onDateChange(
+            shiftUserPeriod(currentDate, periodType, monthStartDay, -1),
+        );
     };
 
     const handleNextPeriod = () => {
-        onDateChange(shiftPeriod(currentDate, periodType, 1));
+        onDateChange(
+            shiftUserPeriod(currentDate, periodType, monthStartDay, 1),
+        );
     };
 
     const handleCurrentPeriod = () => {
@@ -97,7 +105,7 @@ export function PeriodNavigation({
                     variant="outline"
                     className="flex-1 sm:flex-none"
                 >
-                    {formatPeriodLabel(currentDate, periodType, locale)}
+                    {formatPeriodLabel(periodStart, periodType, locale)}
                 </Button>
 
                 <Button
@@ -114,46 +122,6 @@ export function PeriodNavigation({
     );
 }
 
-function shiftPeriod(
-    date: Date,
-    periodType: CashflowPeriodType,
-    amount: 1 | -1,
-): Date {
-    if (periodType === 'quarter') {
-        const quarterStart = startOfQuarter(date);
-
-        return amount > 0
-            ? addQuarters(quarterStart, 1)
-            : subQuarters(quarterStart, 1);
-    }
-
-    if (periodType === 'year') {
-        const yearStart = startOfYear(date);
-
-        return amount > 0 ? addYears(yearStart, 1) : subYears(yearStart, 1);
-    }
-
-    const monthStart = startOfMonth(date);
-
-    return amount > 0 ? addMonths(monthStart, 1) : subMonths(monthStart, 1);
-}
-
-function samePeriod(
-    left: Date,
-    right: Date,
-    periodType: CashflowPeriodType,
-): boolean {
-    if (periodType === 'quarter') {
-        return isSameQuarter(left, right);
-    }
-
-    if (periodType === 'year') {
-        return isSameYear(left, right);
-    }
-
-    return isSameMonth(left, right);
-}
-
 function formatPeriodLabel(
     date: Date,
     periodType: CashflowPeriodType,
diff --git a/resources/js/lib/user-periods.ts b/resources/js/lib/user-periods.ts
new file mode 100644
index 00000000..039683cf
--- /dev/null
+++ b/resources/js/lib/user-periods.ts
@@ -0,0 +1,104 @@
+import {
+    addMonths,
+    addQuarters,
+    addYears,
+    endOfDay,
+    startOfDay,
+    subDays,
+} from 'date-fns';
+
+export type UserMonthStartDay = 1 | 25 | 26 | 27 | 28;
+export type UserPeriodType = 'month' | 'quarter' | 'year';
+
+export const USER_MONTH_START_DAYS: UserMonthStartDay[] = [1, 25, 26, 27, 28];
+
+export function userMonthStartDay(value: unknown): UserMonthStartDay {
+    return USER_MONTH_START_DAYS.includes(value as UserMonthStartDay)
+        ? (value as UserMonthStartDay)
+        : 1;
+}
+
+export function getUserPeriodRange(
+    date: Date,
+    periodType: UserPeriodType,
+    monthStartDay: UserMonthStartDay,
+): { from: Date; to: Date; endInclusive: Date } {
+    if (periodType === 'quarter') {
+        return multiMonthPeriodContaining(date, monthStartDay, 3);
+    }
+
+    if (periodType === 'year') {
+        return multiMonthPeriodContaining(date, monthStartDay, 12);
+    }
+
+    const from = monthStartOnOrBefore(date, monthStartDay);
+    const to = addMonths(from, 1);
+
+    return { from, to, endInclusive: endOfDay(subDays(to, 1)) };
+}
+
+export function shiftUserPeriod(
+    date: Date,
+    periodType: UserPeriodType,
+    monthStartDay: UserMonthStartDay,
+    amount: 1 | -1,
+): Date {
+    const { from } = getUserPeriodRange(date, periodType, monthStartDay);
+
+    if (periodType === 'quarter') {
+        return amount > 0 ? addQuarters(from, 1) : addQuarters(from, -1);
+    }
+
+    if (periodType === 'year') {
+        return amount > 0 ? addYears(from, 1) : addYears(from, -1);
+    }
+
+    return amount > 0 ? addMonths(from, 1) : addMonths(from, -1);
+}
+
+export function sameUserPeriod(
+    left: Date,
+    right: Date,
+    periodType: UserPeriodType,
+    monthStartDay: UserMonthStartDay,
+): boolean {
+    return (
+        getUserPeriodRange(left, periodType, monthStartDay).from.getTime() ===
+        getUserPeriodRange(right, periodType, monthStartDay).from.getTime()
+    );
+}
+
+function multiMonthPeriodContaining(
+    date: Date,
+    monthStartDay: UserMonthStartDay,
+    months: 3 | 12,
+): { from: Date; to: Date; endInclusive: Date } {
+    const anchorMonth =
+        months === 12 ? 0 : Math.floor(date.getMonth() / months) * months;
+    let from = startOfDay(
+        new Date(date.getFullYear(), anchorMonth, monthStartDay),
+    );
+
+    if (from > date) {
+        from = addMonths(from, -months);
+    }
+
+    const to = addMonths(from, months);
+
+    return { from, to, endInclusive: endOfDay(subDays(to, 1)) };
+}
+
+function monthStartOnOrBefore(
+    date: Date,
+    monthStartDay: UserMonthStartDay,
+): Date {
+    let start = startOfDay(
+        new Date(date.getFullYear(), date.getMonth(), monthStartDay),
+    );
+
+    if (start > date) {
+        start = addMonths(start, -1);
+    }
+
+    return start;
+}
diff --git a/resources/js/pages/cashflow/index.tsx b/resources/js/pages/cashflow/index.tsx
index 49b0a9fe..d75bcd2b 100644
--- a/resources/js/pages/cashflow/index.tsx
+++ b/resources/js/pages/cashflow/index.tsx
@@ -7,21 +7,12 @@ import HeadingSmall from '@/components/heading-small';
 import { Card, CardContent, CardHeader, CardTitle } from '@/components/ui/card';
 import { CashflowPeriodType, useCashflowData } from '@/hooks/use-cashflow-data';
 import AppSidebarLayout from '@/layouts/app/app-sidebar-layout';
+import { getUserPeriodRange, userMonthStartDay } from '@/lib/user-periods';
 import { cashflow } from '@/routes';
 import { BreadcrumbItem } from '@/types';
 import { __ } from '@/utils/i18n';
 import { Head, router, usePage } from '@inertiajs/react';
-import {
-    endOfMonth,
-    endOfQuarter,
-    endOfYear,
-    format,
-    getQuarter,
-    parse,
-    startOfMonth,
-    startOfQuarter,
-    startOfYear,
-} from 'date-fns';
+import { format, getQuarter, parse } from 'date-fns';
 import { useEffect, useState } from 'react';
 
 const breadcrumbs: BreadcrumbItem[] = [
@@ -34,6 +25,7 @@ const breadcrumbs: BreadcrumbItem[] = [
 function parsePeriodParam(
     period: string | null,
     periodType: CashflowPeriodType,
+    monthStartDay: number,
 ): Date {
     if (!period) {
         return new Date();
@@ -44,7 +36,11 @@ function parsePeriodParam(
             const match = /^(\d{4})-Q([1-4])$/.exec(period);
 
             if (match) {
-                return new Date(Number(match[1]), (Number(match[2]) - 1) * 3);
+                return new Date(
+                    Number(match[1]),
+                    (Number(match[2]) - 1) * 3,
+                    monthStartDay,
+                );
             }
         }
 
@@ -52,14 +48,18 @@ function parsePeriodParam(
             const match = /^(\d{4})$/.exec(period);
 
             if (match) {
-                return new Date(Number(match[1]), 0);
+                return new Date(Number(match[1]), 0, monthStartDay);
             }
         }
 
         const parsedDate = parse(period, 'yyyy-MM', new Date());
 
         if (!isNaN(parsedDate.getTime())) {
-            return parsedDate;
+            return new Date(
+                parsedDate.getFullYear(),
+                parsedDate.getMonth(),
+                monthStartDay,
+            );
         }
     } catch {
         return new Date();
@@ -68,30 +68,6 @@ function parsePeriodParam(
     return new Date();
 }
 
-function getPeriodRange(
-    currentDate: Date,
-    periodType: CashflowPeriodType,
-): { from: Date; to: Date } {
-    if (periodType === 'quarter') {
-        return {
-            from: startOfQuarter(currentDate),
-            to: endOfQuarter(currentDate),
-        };
-    }
-
-    if (periodType === 'year') {
-        return {
-            from: startOfYear(currentDate),
-            to: endOfYear(currentDate),
-        };
-    }
-
-    return {
-        from: startOfMonth(currentDate),
-        to: endOfMonth(currentDate),
-    };
-}
-
 function formatPeriodParam(
     currentDate: Date,
     periodType: CashflowPeriodType,
@@ -113,19 +89,28 @@ export default function CashflowPage() {
         period: initialPeriod,
         periodType: initialPeriodType,
     } = usePage<{
-        auth: { user: { currency_code: string } };
+        auth: { user: { currency_code: string; month_start_day: number } };
         period: string | null;
         periodType: CashflowPeriodType;
     }>().props;
 
     const [periodType, setPeriodType] =
         useState<CashflowPeriodType>(initialPeriodType);
+    const monthStartDay = userMonthStartDay(auth.user.month_start_day);
 
     const [currentDate, setCurrentDate] = useState<Date>(() =>
-        parsePeriodParam(initialPeriod, initialPeriodType),
+        parsePeriodParam(initialPeriod, initialPeriodType, monthStartDay),
     );
-
-    const period = getPeriodRange(currentDate, periodType);
+    const userPeriod = getUserPeriodRange(
+        currentDate,
+        periodType,
+        monthStartDay,
+    );
+    const period = {
+        from: userPeriod.from,
+        to: userPeriod.endInclusive,
+    };
+    const periodParam = formatPeriodParam(userPeriod.from, periodType);
 
     const {
         summary,
@@ -140,8 +125,6 @@ export default function CashflowPage() {
     });
 
     useEffect(() => {
-        const periodParam = formatPeriodParam(currentDate, periodType);
-
         if (initialPeriod !== periodParam || initialPeriodType !== periodType) {
             router.visit(
                 cashflow({
@@ -154,7 +137,7 @@ export default function CashflowPage() {
                 },
             );
         }
-    }, [currentDate, initialPeriod, initialPeriodType, periodType]);
+    }, [initialPeriod, initialPeriodType, periodParam, periodType]);
 
     return (
         <AppSidebarLayout breadcrumbs={breadcrumbs}>
@@ -172,6 +155,7 @@ export default function CashflowPage() {
                     <PeriodNavigation
                         currentDate={currentDate}
                         periodType={periodType}
+                        monthStartDay={monthStartDay}
                         onDateChange={setCurrentDate}
                         onPeriodTypeChange={setPeriodType}
                     />
diff --git a/resources/js/pages/settings/account.tsx b/resources/js/pages/settings/account.tsx
index 29b0298d..01cb7c96 100644
--- a/resources/js/pages/settings/account.tsx
+++ b/resources/js/pages/settings/account.tsx
@@ -218,6 +218,54 @@ export default function Account({
                                     />
                                 </div>
 
+                                <div className="grid gap-2">
+                                    <Label htmlFor="month_start_day">
+                                        {__('Start of month')}
+                                    </Label>
+
+                                    <Select
+                                        name="month_start_day"
+                                        defaultValue={String(
+                                            auth.user.month_start_day ?? 1,
+                                        )}
+                                        required
+                                    >
+                                        <SelectTrigger className="mt-1 w-full">
+                                            <SelectValue
+                                                placeholder={__(
+                                                    'Select start of month',
+                                                )}
+                                            />
+                                        </SelectTrigger>
+                                        <SelectContent>
+                                            <SelectItem value="1">
+                                                {__('Calendar month (1st)')}
+                                            </SelectItem>
+                                            {[25, 26, 27, 28].map((day) => (
+                                                <SelectItem
+                                                    key={day}
+                                                    value={String(day)}
+                                                >
+                                                    {__('Day :day', {
+                                                        day: String(day),
+                                                    })}
+                                                </SelectItem>
+                                            ))}
+                                        </SelectContent>
+                                    </Select>
+
+                                    <p className="text-sm text-muted-foreground">
+                                        {__(
+                                            'Cashflow periods and analysis will start on this day.',
+                                        )}
+                                    </p>
+
+                                    <InputError
+                                        className="mt-2"
+                                        message={errors.month_start_day}
+                                    />
+                                </div>
+
                                 {mustVerifyEmail &&
                                     auth.user.email_verified_at === null && (
                                         <div>
diff --git a/resources/js/types/index.d.ts b/resources/js/types/index.d.ts
index 72947ac6..28777701 100644
--- a/resources/js/types/index.d.ts
+++ b/resources/js/types/index.d.ts
@@ -101,6 +101,7 @@ export interface User {
     currency_code: CurrencyCode;
     locale: string | null;
     timezone: string | null;
+    month_start_day: 1 | 25 | 26 | 27 | 28;
     avatar?: string;
     email_verified_at: string | null;
     two_factor_enabled?: boolean;
diff --git a/tests/Feature/CashflowAnalyticsTest.php b/tests/Feature/CashflowAnalyticsTest.php
index 42bd965e..25753466 100644
--- a/tests/Feature/CashflowAnalyticsTest.php
+++ b/tests/Feature/CashflowAnalyticsTest.php
@@ -259,6 +259,49 @@ test('cashflow summary includes actual saved and invested amounts', function ()
         ->assertJsonPath('current.investments', 15000);
 });
 
+test('cashflow summary respects custom salary month boundaries', function () {
+    $this->user->update(['month_start_day' => 25]);
+
+    $incomeCategory = Category::factory()->create([
+        'user_id' => $this->user->id,
+        'type' => CategoryType::Income,
+    ]);
+
+    $account = Account::factory()->create(['user_id' => $this->user->id]);
+
+    foreach ([
+        ['date' => '2026-01-24', 'amount' => 10000],
+        ['date' => '2026-01-25', 'amount' => 20000],
+        ['date' => '2026-02-24', 'amount' => 30000],
+        ['date' => '2026-02-25', 'amount' => 40000],
+    ] as $transaction) {
+        Transaction::factory()->create([
+            'user_id' => $this->user->id,
+            'account_id' => $account->id,
+            'category_id' => $incomeCategory->id,
+            'amount' => $transaction['amount'],
+            'transaction_date' => $transaction['date'],
+        ]);
+    }
+
+    $summary = $this->getJson('/api/cashflow/summary?'.http_build_query([
+        'from' => '2026-01-25',
+        'to' => '2026-02-24',
+    ]));
+    $trend = $this->getJson('/api/cashflow/trend?'.http_build_query([
+        'from' => '2026-01-25',
+        'to' => '2026-02-24',
+    ]));
+
+    $summary->assertOk()
+        ->assertJsonPath('current.income', 50000)
+        ->assertJsonPath('previous.income', 10000);
+
+    $trend->assertOk()
+        ->assertJsonPath('data.0.month', '2026-01')
+        ->assertJsonPath('data.0.income', 50000);
+});
+
 test('cashflow summary compares full quarter against previous full quarter', function () {
     $incomeCategory = Category::factory()->create([
         'user_id' => $this->user->id,
diff --git a/tests/Feature/DashboardTest.php b/tests/Feature/DashboardTest.php
index 58481dda..be469c91 100644
--- a/tests/Feature/DashboardTest.php
+++ b/tests/Feature/DashboardTest.php
@@ -82,3 +82,40 @@ test('dashboard top categories roll child spending up into the parent', function
         ->assertJsonPath('props.topCategories.0.category.id', $food->id)
         ->assertJsonPath('props.topCategories.0.amount', 3000);
 });
+
+test('dashboard cashflow summary uses user month start day', function () {
+    $this->travelTo('2026-02-10');
+
+    $user = User::factory()->onboarded()->create(['month_start_day' => 25]);
+    $this->actingAs($user);
+
+    $incomeCategory = Category::factory()->create([
+        'user_id' => $user->id,
+        'type' => CategoryType::Income,
+    ]);
+
+    foreach ([
+        ['date' => '2026-01-24', 'amount' => 10000],
+        ['date' => '2026-01-25', 'amount' => 20000],
+        ['date' => '2026-02-24', 'amount' => 30000],
+    ] as $transaction) {
+        Transaction::factory()->create([
+            'user_id' => $user->id,
+            'category_id' => $incomeCategory->id,
+            'amount' => $transaction['amount'],
+            'transaction_date' => $transaction['date'],
+        ]);
+    }
+
+    $response = $this->get(route('dashboard'));
+
+    $response->assertOk()
+        ->assertInertia(fn ($page) => $page
+            ->component('dashboard')
+            ->missing('cashflowSummary')
+            ->loadDeferredProps(fn ($reload) => $reload
+                ->where('cashflowSummary.current.income', 50000)
+                ->where('cashflowSummary.previous.income', 10000)
+            )
+        );
+});
diff --git a/tests/Feature/Settings/ProfileUpdateTest.php b/tests/Feature/Settings/ProfileUpdateTest.php
index 479c7c35..c0614a79 100644
--- a/tests/Feature/Settings/ProfileUpdateTest.php
+++ b/tests/Feature/Settings/ProfileUpdateTest.php
@@ -21,6 +21,7 @@ test('profile information can be updated', function () {
             'name' => 'Test User',
             'email' => 'test@example.com',
             'currency_code' => 'EUR',
+            'month_start_day' => 25,
         ]);
 
     $response
@@ -33,6 +34,7 @@ test('profile information can be updated', function () {
     expect($user->email)->toBe('test@example.com');
     expect($user->email_verified_at)->toBeNull();
     expect($user->currency_code)->toBe('EUR');
+    expect($user->month_start_day)->toBe(25);
 });
 
 test('profile accepts new latam primary currency', function () {
@@ -44,6 +46,7 @@ test('profile accepts new latam primary currency', function () {
             'name' => 'Test User',
             'email' => 'test@example.com',
             'currency_code' => 'ARS',
+            'month_start_day' => 1,
         ]);
 
     $response
@@ -119,11 +122,27 @@ test('profile rejects bitcoin as primary currency', function () {
             'name' => 'Test User',
             'email' => 'test@example.com',
             'currency_code' => 'BTC',
+            'month_start_day' => 1,
         ]);
 
     $response->assertSessionHasErrors(['currency_code']);
 });
 
+test('profile rejects unsupported month start day', function () {
+    $user = User::factory()->create();
+
+    $response = $this
+        ->actingAs($user)
+        ->patch(route('profile.update'), [
+            'name' => 'Test User',
+            'email' => 'test@example.com',
+            'currency_code' => 'USD',
+            'month_start_day' => 24,
+        ]);
+
+    $response->assertSessionHasErrors(['month_start_day']);
+});
+
 test('email verification status is unchanged when the email address is unchanged', function () {
     $user = User::factory()->create();
 
@@ -133,6 +152,7 @@ test('email verification status is unchanged when the email address is unchanged
             'name' => 'Test User',
             'email' => $user->email,
             'currency_code' => $user->currency_code,
+            'month_start_day' => 1,
         ]);
 
     $response
diff --git a/tests/Feature/UserMonthPeriodServiceTest.php b/tests/Feature/UserMonthPeriodServiceTest.php
new file mode 100644
index 00000000..5b377962
--- /dev/null
+++ b/tests/Feature/UserMonthPeriodServiceTest.php
@@ -0,0 +1,40 @@
+<?php
+
+use App\Models\User;
+use App\Services\UserMonthPeriodService;
+use Carbon\Carbon;
+
+it('returns natural month periods by default', function () {
+    $user = User::factory()->make(['month_start_day' => 1]);
+    $period = app(UserMonthPeriodService::class)->monthContaining($user, Carbon::parse('2026-02-14'));
+
+    expect($period['from']->toDateString())->toBe('2026-02-01')
+        ->and($period['to']->toDateString())->toBe('2026-03-01')
+        ->and($period['end_inclusive']->toDateString())->toBe('2026-02-28');
+});
+
+it('returns salary month periods for custom start days', function () {
+    $user = User::factory()->make(['month_start_day' => 25]);
+    $period = app(UserMonthPeriodService::class)->monthContaining($user, Carbon::parse('2026-02-14'));
+    $previousPeriod = app(UserMonthPeriodService::class)->monthContaining($user, $period['from']->copy()->subDay());
+
+    expect($period['from']->toDateString())->toBe('2026-01-25')
+        ->and($period['to']->toDateString())->toBe('2026-02-25')
+        ->and($period['end_inclusive']->toDateString())->toBe('2026-02-24')
+        ->and($previousPeriod['from']->toDateString())->toBe('2025-12-25')
+        ->and($previousPeriod['to']->toDateString())->toBe('2026-01-25');
+});
+
+it('starts a new salary month on the configured day', function () {
+    $user = User::factory()->make(['month_start_day' => 28]);
+    $period = app(UserMonthPeriodService::class)->monthContaining($user, Carbon::parse('2026-02-28'));
+
+    expect($period['from']->toDateString())->toBe('2026-02-28')
+        ->and($period['to']->toDateString())->toBe('2026-03-28');
+});
+
+it('falls back to the first for invalid stored values', function () {
+    $user = User::factory()->make(['month_start_day' => 2]);
+
+    expect(app(UserMonthPeriodService::class)->startDay($user))->toBe(1);
+});