diff --git a/internal/web/static/js/format.js b/internal/web/static/js/format.js
index c50ba1e..8861f0a 100644
--- a/internal/web/static/js/format.js
+++ b/internal/web/static/js/format.js
@@ -82,15 +82,6 @@ export function addDays(d, n) {
   return r;
 }
 
-// ISO 8601 week number.
-export function isoWeek(d) {
-  const t = new Date(Date.UTC(d.getFullYear(), d.getMonth(), d.getDate()));
-  const day = t.getUTCDay() || 7;
-  t.setUTCDate(t.getUTCDate() + 4 - day);
-  const yearStart = new Date(Date.UTC(t.getUTCFullYear(), 0, 1));
-  return Math.ceil(((t - yearStart) / DAY + 1) / 7);
-}
-
 export const STATUS_LABEL = {
   triggered: 'Triggered',
   acknowledged: 'Acknowledged',