diff --git a/app/components/malio/date/composables/dateWeek.test.ts b/app/components/malio/date/composables/dateWeek.test.ts
new file mode 100644
index 0000000..0d52e5b
--- /dev/null
+++ b/app/components/malio/date/composables/dateWeek.test.ts
@@ -0,0 +1,74 @@
+import {describe, expect, it} from 'vitest'
+import {
+  formatWeekDisplay,
+  isValidIsoWeek,
+  isoWeekToMonday,
+  mondayOf,
+  sundayOf,
+  toIsoWeek,
+} from './dateWeek'
+
+describe('dateWeek', () => {
+  describe('mondayOf / sundayOf', () => {
+    it('returns Monday and Sunday of a midweek date', () => {
+      expect(mondayOf('2026-05-20')).toBe('2026-05-18') // mercredi
+      expect(sundayOf('2026-05-20')).toBe('2026-05-24')
+    })
+    it('keeps Monday on a Monday', () => {
+      expect(mondayOf('2026-05-18')).toBe('2026-05-18')
+    })
+    it('returns the preceding Monday for a Sunday', () => {
+      expect(mondayOf('2026-05-24')).toBe('2026-05-18')
+    })
+  })
+
+  describe('toIsoWeek', () => {
+    it('returns the ISO week of a date', () => {
+      expect(toIsoWeek('2026-05-20')).toBe('2026-W21')
+    })
+    it('handles year boundaries', () => {
+      expect(toIsoWeek('2026-01-01')).toBe('2026-W01')
+      expect(toIsoWeek('2025-12-31')).toBe('2026-W01')
+      expect(toIsoWeek('2027-01-01')).toBe('2026-W53')
+    })
+  })
+
+  describe('isoWeekToMonday', () => {
+    it('returns the Monday of a week string', () => {
+      expect(isoWeekToMonday('2026-W21')).toBe('2026-05-18')
+    })
+    it('round-trips with toIsoWeek', () => {
+      for (const w of ['2026-W01', '2026-W21', '2026-W53', '2024-W09']) {
+        const monday = isoWeekToMonday(w)
+        expect(monday).not.toBeNull()
+        expect(toIsoWeek(monday as string)).toBe(w)
+      }
+    })
+    it('returns null for invalid input', () => {
+      expect(isoWeekToMonday('2026-21')).toBeNull()
+      expect(isoWeekToMonday('2026-W00')).toBeNull()
+      expect(isoWeekToMonday('2026-W54')).toBeNull()
+      expect(isoWeekToMonday('2025-W53')).toBeNull() // 2025 n'a que 52 semaines ISO
+    })
+  })
+
+  describe('isValidIsoWeek', () => {
+    it('accepts a real ISO week', () => {
+      expect(isValidIsoWeek('2026-W21')).toBe(true)
+    })
+    it('rejects malformed or impossible weeks', () => {
+      expect(isValidIsoWeek('2026-21')).toBe(false)
+      expect(isValidIsoWeek('2026-W00')).toBe(false)
+      expect(isValidIsoWeek('2026-W54')).toBe(false)
+    })
+  })
+
+  describe('formatWeekDisplay', () => {
+    it('formats a week as a human label', () => {
+      expect(formatWeekDisplay('2026-W21')).toBe('Semaine 21 (18/05 → 24/05/2026)')
+    })
+    it('returns empty string for invalid input', () => {
+      expect(formatWeekDisplay('2026-W54')).toBe('')
+    })
+  })
+})
diff --git a/app/components/malio/date/composables/dateWeek.ts b/app/components/malio/date/composables/dateWeek.ts
new file mode 100644
index 0000000..ba17ed0
--- /dev/null
+++ b/app/components/malio/date/composables/dateWeek.ts
@@ -0,0 +1,67 @@
+import {formatIsoToDisplay} from './dateFormat'
+
+const parseUtc = (iso: string): Date => {
+  const [y, m, d] = iso.split('-').map(Number)
+  return new Date(Date.UTC(y, m - 1, d))
+}
+
+const toIso = (d: Date): string => {
+  const y = d.getUTCFullYear()
+  const m = String(d.getUTCMonth() + 1).padStart(2, '0')
+  const day = String(d.getUTCDate()).padStart(2, '0')
+  return `${y}-${m}-${day}`
+}
+
+export function mondayOf(iso: string): string {
+  const d = parseUtc(iso)
+  const dayNum = d.getUTCDay() || 7 // dimanche = 7
+  d.setUTCDate(d.getUTCDate() - (dayNum - 1))
+  return toIso(d)
+}
+
+export function sundayOf(iso: string): string {
+  const d = parseUtc(mondayOf(iso))
+  d.setUTCDate(d.getUTCDate() + 6)
+  return toIso(d)
+}
+
+export function toIsoWeek(iso: string): string {
+  const d = parseUtc(iso)
+  const dayNum = d.getUTCDay() || 7
+  d.setUTCDate(d.getUTCDate() + 4 - dayNum) // jeudi de la semaine
+  const isoYear = d.getUTCFullYear()
+  const yearStart = new Date(Date.UTC(isoYear, 0, 1))
+  const week = Math.ceil((((d.getTime() - yearStart.getTime()) / 86400000) + 1) / 7)
+  return `${isoYear}-W${String(week).padStart(2, '0')}`
+}
+
+export function isoWeekToMonday(week: string): string | null {
+  const m = /^(\d{4})-W(\d{2})$/.exec(week)
+  if (!m) return null
+  const year = Number(m[1])
+  const w = Number(m[2])
+  if (w < 1 || w > 53) return null
+  // Lundi de la semaine 1 = lundi de la semaine contenant le 4 janvier
+  const jan4 = new Date(Date.UTC(year, 0, 4))
+  const jan4Day = jan4.getUTCDay() || 7
+  const monday = new Date(jan4)
+  monday.setUTCDate(jan4.getUTCDate() - (jan4Day - 1) + (w - 1) * 7)
+  const iso = toIso(monday)
+  // Garde-fou : la semaine 53 n'existe pas pour toutes les années
+  if (toIsoWeek(iso) !== week) return null
+  return iso
+}
+
+export function isValidIsoWeek(week: string): boolean {
+  return isoWeekToMonday(week) !== null
+}
+
+export function formatWeekDisplay(week: string): string {
+  const monday = isoWeekToMonday(week)
+  if (!monday) return ''
+  const sunday = sundayOf(monday)
+  const w = Number(week.slice(6))
+  const startDdMm = formatIsoToDisplay(monday).slice(0, 5) // "18/05"
+  const endFull = formatIsoToDisplay(sunday) // "24/05/2026"
+  return `Semaine ${w} (${startDdMm} → ${endFull})`
+}