diff --git a/app/components/malio/date/composables/dateRange.test.ts b/app/components/malio/date/composables/dateRange.test.ts
new file mode 100644
index 0000000..d6e5ab7
--- /dev/null
+++ b/app/components/malio/date/composables/dateRange.test.ts
@@ -0,0 +1,57 @@
+import {describe, expect, it} from 'vitest'
+import {dayRangeRole, normalizeRange, resolveRangeBounds} from './dateRange'
+
+describe('dateRange', () => {
+  describe('normalizeRange', () => {
+    it('keeps an already ordered pair', () => {
+      expect(normalizeRange('2026-05-19', '2026-05-25')).toEqual({start: '2026-05-19', end: '2026-05-25'})
+    })
+    it('swaps a reversed pair', () => {
+      expect(normalizeRange('2026-05-25', '2026-05-19')).toEqual({start: '2026-05-19', end: '2026-05-25'})
+    })
+    it('handles an equal pair', () => {
+      expect(normalizeRange('2026-05-19', '2026-05-19')).toEqual({start: '2026-05-19', end: '2026-05-19'})
+    })
+  })
+
+  describe('resolveRangeBounds', () => {
+    it('returns null without a start', () => {
+      expect(resolveRangeBounds(null, null, null)).toBeNull()
+    })
+    it('returns a single-point range when only start is set', () => {
+      expect(resolveRangeBounds('2026-05-19', null, null)).toEqual({lo: '2026-05-19', hi: '2026-05-19'})
+    })
+    it('orders start and committed end', () => {
+      expect(resolveRangeBounds('2026-05-19', '2026-05-25', null)).toEqual({lo: '2026-05-19', hi: '2026-05-25'})
+    })
+    it('uses preview when end is not set', () => {
+      expect(resolveRangeBounds('2026-05-19', null, '2026-05-22')).toEqual({lo: '2026-05-19', hi: '2026-05-22'})
+    })
+    it('inverts when preview is before start', () => {
+      expect(resolveRangeBounds('2026-05-19', null, '2026-05-10')).toEqual({lo: '2026-05-10', hi: '2026-05-19'})
+    })
+    it('prioritises committed end over preview', () => {
+      expect(resolveRangeBounds('2026-05-19', '2026-05-25', '2026-05-30')).toEqual({lo: '2026-05-19', hi: '2026-05-25'})
+    })
+  })
+
+  describe('dayRangeRole', () => {
+    const bounds = {lo: '2026-05-19', hi: '2026-05-25'}
+    it('returns none without bounds', () => {
+      expect(dayRangeRole('2026-05-20', null)).toBe('none')
+    })
+    it('returns single when lo === hi and matches', () => {
+      expect(dayRangeRole('2026-05-19', {lo: '2026-05-19', hi: '2026-05-19'})).toBe('single')
+      expect(dayRangeRole('2026-05-20', {lo: '2026-05-19', hi: '2026-05-19'})).toBe('none')
+    })
+    it('returns start, end and in-range', () => {
+      expect(dayRangeRole('2026-05-19', bounds)).toBe('start')
+      expect(dayRangeRole('2026-05-25', bounds)).toBe('end')
+      expect(dayRangeRole('2026-05-22', bounds)).toBe('in-range')
+    })
+    it('returns none outside the bounds', () => {
+      expect(dayRangeRole('2026-05-10', bounds)).toBe('none')
+      expect(dayRangeRole('2026-05-30', bounds)).toBe('none')
+    })
+  })
+})
diff --git a/app/components/malio/date/composables/dateRange.ts b/app/components/malio/date/composables/dateRange.ts
new file mode 100644
index 0000000..5dd62b5
--- /dev/null
+++ b/app/components/malio/date/composables/dateRange.ts
@@ -0,0 +1,31 @@
+export type DateRangeValue = {start: string; end: string}
+
+export function normalizeRange(a: string, b: string): DateRangeValue {
+  return a <= b ? {start: a, end: b} : {start: b, end: a}
+}
+
+export function resolveRangeBounds(
+  start: string | null,
+  end: string | null,
+  preview: string | null,
+): {lo: string; hi: string} | null {
+  if (!start) return null
+  const other = end ?? preview
+  if (!other) return {lo: start, hi: start}
+  return start <= other ? {lo: start, hi: other} : {lo: other, hi: start}
+}
+
+export type DayRangeRole = 'none' | 'single' | 'start' | 'end' | 'in-range'
+
+export function dayRangeRole(
+  iso: string,
+  bounds: {lo: string; hi: string} | null,
+): DayRangeRole {
+  if (!bounds) return 'none'
+  const {lo, hi} = bounds
+  if (lo === hi) return iso === lo ? 'single' : 'none'
+  if (iso === lo) return 'start'
+  if (iso === hi) return 'end'
+  if (iso > lo && iso < hi) return 'in-range'
+  return 'none'
+}