diff --git a/frontend/src/utils/fiscalWeek.js b/frontend/src/utils/fiscalWeek.js
new file mode 100644
index 0000000..883fed3
--- /dev/null
+++ b/frontend/src/utils/fiscalWeek.js
@@ -0,0 +1,48 @@
+/**
+ * Fiscal week, as the classic ASP site computed it.
+ *
+ * That site called it "Fiscal Week" and calculated an ISO 8601 week number
+ * (includes/leftsidebar.asp): week 1 is the week containing 4 January, weeks
+ * start on Monday, and the year is decided by that week's Thursday. This is a
+ * faithful port - the label and the arithmetic both come from there.
+ *
+ * Worth knowing if the numbers are ever questioned: a true GE fiscal calendar
+ * need not line up with ISO weeks. Nobody has asked for a different rule, and
+ * changing it here would silently disagree with the classic site people still
+ * compare against, so it stays ISO until someone says otherwise.
+ */
+
+/**
+ * ISO 8601 week number for a date (1-53).
+ *
+ * Works in local time deliberately: the number people quote is the one on the
+ * wall where they are, and a UTC-based week rolls over hours early in the
+ * evening at a US site.
+ */
+export function fiscalWeek(date = new Date()) {
+ const day = new Date(date.getFullYear(), date.getMonth(), date.getDate())
+
+ // The Thursday of this week decides which year the week belongs to, which is
+ // what makes late December and early January land in the right year.
+ const dayOfWeek = (day.getDay() + 6) % 7 // 0 = Monday
+ const thursday = new Date(day)
+ thursday.setDate(day.getDate() + 3 - dayOfWeek)
+
+ // Week 1 is the week containing 4 January; find its Monday.
+ const jan4 = new Date(thursday.getFullYear(), 0, 4)
+ const jan4DayOfWeek = (jan4.getDay() + 6) % 7
+ const week1Monday = new Date(jan4)
+ week1Monday.setDate(jan4.getDate() - jan4DayOfWeek)
+
+ const days = Math.round((thursday - week1Monday) / 86400000)
+ return Math.floor(days / 7) + 1
+}
+
+/** The year the week belongs to, which is not always the calendar year. */
+export function fiscalWeekYear(date = new Date()) {
+ const day = new Date(date.getFullYear(), date.getMonth(), date.getDate())
+ const dayOfWeek = (day.getDay() + 6) % 7
+ const thursday = new Date(day)
+ thursday.setDate(day.getDate() + 3 - dayOfWeek)
+ return thursday.getFullYear()
+}
diff --git a/frontend/src/utils/fiscalWeek.spec.js b/frontend/src/utils/fiscalWeek.spec.js
new file mode 100644
index 0000000..a65888a
--- /dev/null
+++ b/frontend/src/utils/fiscalWeek.spec.js
@@ -0,0 +1,49 @@
+import { describe, it, expect } from 'vitest'
+import { fiscalWeek, fiscalWeekYear } from './fiscalWeek'
+
+/**
+ * The number has to match what the classic ASP site shows, because people will
+ * have both open. The awkward cases are all at the year boundary, which is
+ * exactly where a naive "day of year / 7" gets it wrong.
+ */
+describe('fiscalWeek', () => {
+ it('counts the week containing 4 January as week 1', () => {
+ expect(fiscalWeek(new Date(2026, 0, 4))).toBe(1)
+ })
+
+ it('puts a late-December date in week 1 of the NEXT year', () => {
+ // 2025-12-29 is a Monday; its Thursday falls in 2026, so it is 2026 week 1.
+ expect(fiscalWeek(new Date(2025, 11, 29))).toBe(1)
+ expect(fiscalWeekYear(new Date(2025, 11, 29))).toBe(2026)
+ })
+
+ it('puts an early-January date in the LAST week of the previous year', () => {
+ // 2027-01-01 is a Friday; its Thursday is 2026-12-31, so it is 2026 week 53.
+ expect(fiscalWeek(new Date(2027, 0, 1))).toBe(53)
+ expect(fiscalWeekYear(new Date(2027, 0, 1))).toBe(2026)
+ })
+
+ it('holds the same number all week, Monday through Sunday', () => {
+ const monday = new Date(2026, 7, 10)
+ const week = fiscalWeek(monday)
+ for (let i = 0; i < 7; i++) {
+ const day = new Date(2026, 7, 10 + i)
+ expect(fiscalWeek(day)).toBe(week)
+ }
+ })
+
+ it('increments the following Monday', () => {
+ expect(fiscalWeek(new Date(2026, 7, 17))).toBe(fiscalWeek(new Date(2026, 7, 10)) + 1)
+ })
+
+ it('gives a 53-week year its 53rd week', () => {
+ // 2026 starts on a Thursday, so it runs to 53 weeks.
+ expect(fiscalWeek(new Date(2026, 11, 31))).toBe(53)
+ })
+
+ it('is not fooled by a time of day', () => {
+ const morning = new Date(2026, 7, 12, 6, 0, 0)
+ const nearMidnight = new Date(2026, 7, 12, 23, 59, 0)
+ expect(fiscalWeek(morning)).toBe(fiscalWeek(nearMidnight))
+ })
+})
diff --git a/frontend/src/views/AppLayout.vue b/frontend/src/views/AppLayout.vue
index bc8146d..19b4a8c 100644
--- a/frontend/src/views/AppLayout.vue
+++ b/frontend/src/views/AppLayout.vue
@@ -4,6 +4,11 @@