diff --git a/index.html b/index.html
index 06fb7b2..80a38b9 100644
--- a/index.html
+++ b/index.html
@@ -122,12 +122,11 @@ function fmtAmt(n) {
 }
 function defaultPeriod() {
   const d = new Date();
-  const lastDay = new Date(d.getFullYear(), d.getMonth()+1, 0).getDate() === d.getDate();
-  const y = lastDay ? d.getFullYear() : (d.getMonth() === 0 ? d.getFullYear()-1 : d.getFullYear());
-  const m = lastDay ? d.getMonth() : (d.getMonth() === 0 ? 11 : d.getMonth()-1);
-  const from = new Date(y, m, 1);
-  const to = new Date(y, m+1, 0);
-  return { from: from.toISOString().slice(0,10), to: to.toISOString().slice(0,10) };
+  const isLastDay = d.getDate() === new Date(d.getFullYear(), d.getMonth() + 1, 0).getDate();
+  const y = isLastDay ? d.getFullYear() : (d.getMonth() === 0 ? d.getFullYear() - 1 : d.getFullYear());
+  const m = isLastDay ? d.getMonth() : (d.getMonth() === 0 ? 11 : d.getMonth() - 1);
+  const fmt = dt => `${dt.getFullYear()}-${String(dt.getMonth()+1).padStart(2,'0')}-${String(dt.getDate()).padStart(2,'0')}`;
+  return { from: fmt(new Date(y, m, 1)), to: fmt(new Date(y, m + 1, 0)) };
 }
 
 // ========== CONFIG ==========