diff --git a/src/__tests__/date-validation.test.ts b/src/__tests__/date-validation.test.ts
new file mode 100644
index 00000000..a247b028
--- /dev/null
+++ b/src/__tests__/date-validation.test.ts
@@ -0,0 +1,88 @@
+import { describe, expect, it } from 'vitest';
+import { apiDateString, dateStringForFormat } from '$lib/domain/shared';
+import { maintenanceFormSchema } from '$lib/domain/maintenance';
+import { complianceFormSchema } from '$lib/domain/compliance';
+
+describe('localized date validation', () => {
+  it('accepts days greater than 12 in day-first formats', () => {
+    expect(dateStringForFormat('dd/MM/yyyy').safeParse('13/08/2026').success).toBe(true);
+    expect(dateStringForFormat('dd/MM/yyyy').safeParse('31/12/2026').success).toBe(true);
+  });
+
+  it('validates against the configured field order', () => {
+    expect(dateStringForFormat('MM/dd/yyyy').safeParse('08/13/2026').success).toBe(true);
+    expect(dateStringForFormat('MM/dd/yyyy').safeParse('13/08/2026').success).toBe(false);
+  });
+
+  it('rejects impossible and partially matching dates', () => {
+    const schema = dateStringForFormat('dd/MM/yyyy');
+    expect(schema.safeParse('31/02/2026').success).toBe(false);
+    expect(schema.safeParse('13/08/2026 trailing').success).toBe(false);
+    expect(schema.safeParse('').success).toBe(false);
+  });
+
+  it('rejects calendar dates that JavaScript would silently normalize', () => {
+    expect(apiDateString.safeParse('2026-02-31').success).toBe(false);
+    expect(apiDateString.safeParse('2026-08-13T12:00:00.000Z').success).toBe(true);
+  });
+
+  it('uses localized validation in the maintenance form schema', () => {
+    const result = maintenanceFormSchema('dd/MM/yyyy').safeParse({
+      id: null,
+      vehicleId: '123e4567-e89b-42d3-a456-426614174000',
+      date: '13/08/2026',
+      odometer: 1,
+      serviceCenter: 'Garage',
+      cost: 0,
+      notes: null,
+      attachment: null
+    });
+
+    expect(result.success).toBe(true);
+  });
+
+  it('compares localized compliance dates chronologically', () => {
+    const base = {
+      id: null,
+      vehicleId: '123e4567-e89b-42d3-a456-426614174000',
+      type: 'insurance' as const,
+      otherLabel: null,
+      documentNumber: 'ABC123',
+      issuer: 'Insurer',
+      startDate: '13/08/2026',
+      recurrenceType: 'none' as const,
+      recurrenceInterval: 1,
+      cost: null,
+      notes: null,
+      attachment: null
+    };
+
+    expect(
+      complianceFormSchema('dd/MM/yyyy').safeParse({ ...base, endDate: '14/08/2026' }).success
+    ).toBe(true);
+    expect(
+      complianceFormSchema('dd/MM/yyyy').safeParse({ ...base, endDate: '12/08/2026' }).success
+    ).toBe(false);
+  });
+
+  it('does not reverse valid ambiguous dates in day-first formats', () => {
+    const base = {
+      id: null,
+      vehicleId: '123e4567-e89b-42d3-a456-426614174000',
+      type: 'insurance' as const,
+      otherLabel: null,
+      documentNumber: 'ABC123',
+      issuer: 'Insurer',
+      startDate: '10/03/2026',
+      recurrenceType: 'none' as const,
+      recurrenceInterval: 1,
+      cost: null,
+      notes: null,
+      attachment: null
+    };
+
+    expect(
+      complianceFormSchema('dd/MM/yyyy').safeParse({ ...base, endDate: '03/10/2026' }).success
+    ).toBe(true);
+  });
+});
diff --git a/src/lib/components/dashboard/StackedAreaChart.svelte b/src/lib/components/dashboard/StackedAreaChart.svelte
index 3ba00cee..e68e65fc 100644
--- a/src/lib/components/dashboard/StackedAreaChart.svelte
+++ b/src/lib/components/dashboard/StackedAreaChart.svelte
@@ -9,6 +9,7 @@
   import LegendInfoGroup from '$appui/LegendInfoGroup.svelte';
   import CircleSlash2 from '@lucide/svelte/icons/circle-slash-2';
   import Skeleton from '$lib/components/ui/skeleton/skeleton.svelte';
+  import { formatCurrency } from '$lib/helper/format.helper';
 
   let {
     data,
@@ -38,7 +39,7 @@
       format: (v: Date) => v.toLocaleDateString('en-IN', { month: 'short', year: '2-digit' })
     },
     yAxis: {
-      format: (v: number) => `$${v.toFixed(0)}`
+      format: (v: number) => formatCurrency(v)
     },
     grid: {
       style: 'stroke-dasharray: 2',
@@ -104,7 +105,7 @@
             {#snippet formatter({ value, name })}
               <span class="text-muted-foreground">{name}</span>
               <span class="font-mono font-medium tabular-nums">
-                {typeof value === 'number' ? `$${value.toFixed(2)}` : value}
+                {typeof value === 'number' ? formatCurrency(value) : value}
               </span>
             {/snippet}
           </Chart.Tooltip>
diff --git a/src/lib/components/feature/compliance/ComplianceForm.svelte b/src/lib/components/feature/compliance/ComplianceForm.svelte
index 593f5762..e6196e56 100644
--- a/src/lib/components/feature/compliance/ComplianceForm.svelte
+++ b/src/lib/components/feature/compliance/ComplianceForm.svelte
@@ -11,7 +11,7 @@
   import { createSheetForm } from '$lib/composables/sheet-form.svelte';
   import * as m from '$lib/paraglide/messages';
   import {
-    complianceSchema,
+    complianceFormSchema,
     COMPLIANCE_TYPES,
     COMPLIANCE_RECURRENCE_TYPES,
     getComplianceRecurrenceTypeLabel,
@@ -20,6 +20,7 @@
     getComplianceDocumentNumberLabel,
     getComplianceIssuerLabel
   } from '$lib/domain/compliance';
+  import configs from '$stores/config.svelte';
   import { FileDropZone, AutocompleteInput } from '$lib/components/app';
   import { getComplianceIssuerSuggestions } from '$lib/services/autocomplete.service';
   import Banknote from '@lucide/svelte/icons/banknote';
@@ -45,7 +46,7 @@
   );
 
   const sf = createSheetForm({
-    schema: complianceSchema,
+    schema: complianceFormSchema(configs.dateFormat),
     onUpdated: async ({ form: f }) => {
       if (f.valid) {
         sf.processing = true;
diff --git a/src/lib/components/feature/fuel/FuelLogForm.svelte b/src/lib/components/feature/fuel/FuelLogForm.svelte
index ff4fe7e7..c513b824 100644
--- a/src/lib/components/feature/fuel/FuelLogForm.svelte
+++ b/src/lib/components/feature/fuel/FuelLogForm.svelte
@@ -16,7 +16,8 @@
   import { fuelLogStore } from '$stores/fuel-log.svelte';
   import { createSheetForm } from '$lib/composables/sheet-form.svelte';
   import { FileDropZone } from '$lib/components/app';
-  import { fuelSchema } from '$lib/domain/fuel';
+  import { fuelFormSchema } from '$lib/domain/fuel';
+  import configs from '$stores/config.svelte';
   import Banknote from '@lucide/svelte/icons/banknote';
   import Calendar1 from '@lucide/svelte/icons/calendar-1';
   import CircleGauge from '@lucide/svelte/icons/circle-gauge';
@@ -66,7 +67,7 @@
   );
 
   const sf = createSheetForm({
-    schema: fuelSchema,
+    schema: fuelFormSchema(configs.dateFormat),
     validationMethod: 'onsubmit',
     onUpdated: async ({ form: f }) => {
       if (f.valid) {
diff --git a/src/lib/components/feature/maintenance/MaintenanceForm.svelte b/src/lib/components/feature/maintenance/MaintenanceForm.svelte
index ca9820e1..7a8726d1 100644
--- a/src/lib/components/feature/maintenance/MaintenanceForm.svelte
+++ b/src/lib/components/feature/maintenance/MaintenanceForm.svelte
@@ -5,7 +5,8 @@
   import Input from '$appui/input.svelte';
   import { Textarea } from '$ui/textarea';
   import { formatDate, parseDate } from '$lib/helper/format.helper';
-  import { maintenanceSchema } from '$lib/domain/maintenance';
+  import { maintenanceFormSchema } from '$lib/domain/maintenance';
+  import configs from '$stores/config.svelte';
   import Banknote from '@lucide/svelte/icons/banknote';
   import Hammer from '@lucide/svelte/icons/hammer';
   import CircleGauge from '@lucide/svelte/icons/circle-gauge';
@@ -34,7 +35,7 @@
   );
 
   const sf = createSheetForm({
-    schema: maintenanceSchema,
+    schema: maintenanceFormSchema(configs.dateFormat),
     onUpdated: async ({ form: f }) => {
       if (f.valid) {
         sf.processing = true;
diff --git a/src/lib/components/feature/reminder/ReminderForm.svelte b/src/lib/components/feature/reminder/ReminderForm.svelte
index c17f82a2..b72bff52 100644
--- a/src/lib/components/feature/reminder/ReminderForm.svelte
+++ b/src/lib/components/feature/reminder/ReminderForm.svelte
@@ -7,11 +7,12 @@
     REMINDER_TYPES,
     REMINDER_SCHEDULES,
     REMINDER_RECURRENCE_TYPES,
-    reminderSchema,
+    reminderFormSchema,
     getReminderScheduleLabel,
     getRecurrenceTypeLabel,
     getReminderTypeLabel
   } from '$lib/domain/reminder';
+  import configs from '$stores/config.svelte';
   import { createSheetForm } from '$lib/composables/sheet-form.svelte';
   import { sheetStore } from '$stores/sheet.svelte';
   import SubmitButton from '$appui/SubmitButton.svelte';
@@ -35,7 +36,7 @@
   let { data }: { data?: Partial<Reminder> } = $props();
 
   const sf = createSheetForm({
-    schema: reminderSchema,
+    schema: reminderFormSchema(configs.dateFormat),
     onUpdated: async ({ form: f }) => {
       if (f.valid) {
         sf.processing = true;
diff --git a/src/lib/domain/compliance.ts b/src/lib/domain/compliance.ts
index 8492746b..b7186f25 100644
--- a/src/lib/domain/compliance.ts
+++ b/src/lib/domain/compliance.ts
@@ -5,7 +5,13 @@ import Leaf from '@lucide/svelte/icons/leaf';
 import ClipboardCheck from '@lucide/svelte/icons/clipboard-check';
 import FileText from '@lucide/svelte/icons/file-text';
 import Shapes from '@lucide/svelte/icons/shapes';
-import { apiDateString, optionalApiDateString } from './shared';
+import {
+  apiDateString,
+  dateStringForFormat,
+  optionalApiDateString,
+  optionalDateStringForFormat
+} from './shared';
+import { parseWithFormat } from '$lib/helper/date.helper';
 import { getNextDueDate } from '$lib/helper/recurrence.helper';
 
 /**
@@ -188,17 +194,22 @@ export const complianceSchema = z
       return !!data.otherLabel && data.otherLabel.trim().length > 0;
     },
     { message: 'Please name the compliance type', path: ['otherLabel'] }
-  )
-  .refine(
-    (data) => {
-      if (data.recurrenceType === undefined) return true;
-      if (data.recurrenceType !== 'none') return true;
-      if (data.endDate === undefined) return true;
-      if (!data.endDate) return false;
-      if (!data.startDate) return true;
-      return new Date(data.endDate) > new Date(data.startDate);
-    },
-    { message: 'End date must be after start date when recurrence is fixed' }
   );
 
 export type ComplianceSchema = typeof complianceSchema;
+
+export const complianceFormSchema = (dateFormat: string) =>
+  complianceSchema
+    .safeExtend({
+      startDate: dateStringForFormat(dateFormat),
+      endDate: optionalDateStringForFormat(dateFormat)
+    })
+    .refine(
+      (data) => {
+        if (data.recurrenceType !== 'none' || !data.startDate || !data.endDate) return true;
+        const startDate = parseWithFormat(data.startDate, dateFormat);
+        const endDate = parseWithFormat(data.endDate, dateFormat);
+        return !!startDate && !!endDate && endDate > startDate;
+      },
+      { message: 'End date must be after start date when recurrence is fixed' }
+    );
diff --git a/src/lib/domain/fuel.ts b/src/lib/domain/fuel.ts
index 0e923b96..89ca4323 100644
--- a/src/lib/domain/fuel.ts
+++ b/src/lib/domain/fuel.ts
@@ -1,5 +1,5 @@
 import { z } from 'zod';
-import { apiDateString } from './shared';
+import { apiDateString, dateStringForFormat } from './shared';
 
 export interface FuelLog {
   id: string | null;
@@ -34,4 +34,7 @@ export const fuelSchema = z.object({
   attachment: z.string().nullable()
 });
 
+export const fuelFormSchema = (dateFormat: string) =>
+  fuelSchema.extend({ date: dateStringForFormat(dateFormat) });
+
 export type FuelSchema = typeof fuelSchema;
diff --git a/src/lib/domain/maintenance.ts b/src/lib/domain/maintenance.ts
index f1383893..3a157d93 100644
--- a/src/lib/domain/maintenance.ts
+++ b/src/lib/domain/maintenance.ts
@@ -1,5 +1,5 @@
 import { z } from 'zod';
-import { apiDateString } from './shared';
+import { apiDateString, dateStringForFormat } from './shared';
 
 export interface MaintenanceLog {
   id: string | null;
@@ -29,4 +29,7 @@ export const maintenanceSchema = z.object({
   attachment: z.string().nullable()
 });
 
+export const maintenanceFormSchema = (dateFormat: string) =>
+  maintenanceSchema.extend({ date: dateStringForFormat(dateFormat) });
+
 export type MaintenanceSchema = typeof maintenanceSchema;
diff --git a/src/lib/domain/reminder.ts b/src/lib/domain/reminder.ts
index 65deaccd..bd5e6a02 100644
--- a/src/lib/domain/reminder.ts
+++ b/src/lib/domain/reminder.ts
@@ -1,5 +1,10 @@
 import { z } from 'zod';
-import { apiDateString, optionalApiDateString } from './shared';
+import {
+  apiDateString,
+  dateStringForFormat,
+  optionalApiDateString,
+  optionalDateStringForFormat
+} from './shared';
 
 export const REMINDER_TYPES = {
   maintenance: 'maintenance',
@@ -137,4 +142,10 @@ export const reminderSchema = z.object({
   isCompleted: z.boolean().default(false)
 });
 
+export const reminderFormSchema = (dateFormat: string) =>
+  reminderSchema.extend({
+    dueDate: dateStringForFormat(dateFormat),
+    recurrenceEndDate: optionalDateStringForFormat(dateFormat)
+  });
+
 export type ReminderSchema = typeof reminderSchema;
diff --git a/src/lib/domain/shared.ts b/src/lib/domain/shared.ts
index 502cfd0f..c147f128 100644
--- a/src/lib/domain/shared.ts
+++ b/src/lib/domain/shared.ts
@@ -1,17 +1,33 @@
 import { z } from 'zod';
+import { parseWithFormat } from '$lib/helper/date.helper';
+import { format, isValid, parseISO } from 'date-fns';
 
 /**
- * Validates date strings accepted by the API: anything the Date
- * constructor can parse (ISO 8601 payloads from JSON-serialized Dates).
+ * Validates ISO 8601 date strings accepted by the API, including payloads
+ * produced by JSON-serialized Dates.
  * Display-format validation for forms lives in format.helper (client-only).
  */
 export const apiDateString = z
   .string()
-  .refine((val) => !Number.isNaN(new Date(val).getTime()), 'Invalid date format');
+  .refine((value) => isValid(parseISO(value)), 'Invalid date format');
 
 /** Nullable/optional variant for fields that can be empty or omitted. */
 export const optionalApiDateString = apiDateString.nullable().optional();
 
+/** Validates a date exactly as it is displayed in a localized form. */
+export const dateStringForFormat = (dateFormat: string) =>
+  z.string().refine(
+    (value) => {
+      const parsed = parseWithFormat(value, dateFormat);
+      return parsed !== null && format(parsed, dateFormat) === value;
+    },
+    { message: `Invalid date. Expected format: ${dateFormat}` }
+  );
+
+/** Nullable/optional localized date used by form-only schemas. */
+export const optionalDateStringForFormat = (dateFormat: string) =>
+  dateStringForFormat(dateFormat).nullable().optional();
+
 export type DataPoint = {
   x: Date | string;
   y: number | null;
diff --git a/src/routes/(app)/fuel/+page.svelte b/src/routes/(app)/fuel/+page.svelte
index a4365f31..dbc4e0c9 100644
--- a/src/routes/(app)/fuel/+page.svelte
+++ b/src/routes/(app)/fuel/+page.svelte
@@ -7,7 +7,7 @@
   import { fuelLogStore } from '$stores/fuel-log.svelte';
   import { chartStore } from '$stores/chart.svelte';
   import { ACCENT } from '$lib/helper/accent-color.helper';
-  import { formatMileage } from '$lib/helper/format.helper';
+  import { formatCurrency, formatMileage } from '$lib/helper/format.helper';
   import VehicleTrendChart from '$feature/overview/VehicleTrendChart.svelte';
   import FuelLogTab from '$feature/fuel/FuelLogTab.svelte';
   import { Features } from '$lib/helper/feature.helper';
@@ -52,7 +52,7 @@
       <StatCard
         icon={DollarSign}
         label={fuel_stat_spent()}
-        value={totalCost > 0 ? `$${totalCost.toFixed(2)}` : '--'}
+        value={totalCost > 0 ? formatCurrency(totalCost) : '--'}
         color={ACCENT.ochre.gradient}
       />
       <StatCard