diff --git a/src/screens/supplier/Runs.tsx b/src/screens/supplier/Runs.tsx
index c57f834..1c7f446 100644
--- a/src/screens/supplier/Runs.tsx
+++ b/src/screens/supplier/Runs.tsx
@@ -8,6 +8,15 @@ import { DataTable, StateBadge } from '../../components/widgets';
 import { date, inr, mt } from '../../format';
 import { useScope } from './scope';
 
+/** The previous calendar month, the natural default for a monthly run. */
+function lastMonth(): { period_from: string; period_to: string } {
+  const now = new Date();
+  const from = new Date(now.getFullYear(), now.getMonth() - 1, 1);
+  const to = new Date(now.getFullYear(), now.getMonth(), 0);
+  const iso = (d: Date) => `${d.getFullYear()}-${String(d.getMonth() + 1).padStart(2, '0')}-${String(d.getDate()).padStart(2, '0')}`;
+  return { period_from: iso(from), period_to: iso(to) };
+}
+
 export function Runs() {
   const { client } = useZino();
   const scope = useScope();
@@ -43,7 +52,7 @@ export function Runs() {
           cols={[{ key: 'dealer_name', label: 'Dealer' }, { key: 'scheme_name', label: 'Scheme', render: (r) => `${String(r.scheme_name)} · ${String(r.component_name)}` }, { key: 'measured_qty', label: 'MT', align: 'right', render: (r) => mt(r.measured_qty, 0) }, { key: 'slab_label', label: 'Slab', render: (r) => (r.gate_passed ? String(r.slab_label ?? '') : <span className="text-warn">{String(r.gate_reason ?? '')}</span>) }, { key: 'incentive_amount', label: 'Amount', align: 'right', render: (r) => inr(r.incentive_amount) }, { key: 'status', label: 'Status', render: (r) => <Badge tone={r.status === 'FINAL' ? 'emerald' : 'amber'}>{String(r.status)}</Badge> }]} />
       </Modal>
       <ActivityForm open={req} onClose={() => setReq(false)} workflow={WF.RUN} activityUid={ACT.RUN_REQUEST} title="Request a settlement run" subtitle="Pick the period; the engine computes it provisionally and the Analyst reports."
-        prefill={{ frequency: 'MONTHLY', period_from: '2026-09-01', period_to: '2026-09-30' }} onDone={() => runs.refetch()} />
+        prefill={{ frequency: 'MONTHLY', ...lastMonth() }} onDone={() => runs.refetch()} />
       {decide && <ActivityForm open onClose={() => setDecide(null)} workflow={WF.RUN} activityUid={decide.act} instanceId={decide.id} title={decide.title} danger={decide.danger} onDone={() => runs.refetch()} />}
     </div>
   );