diff --git a/App/components/po/po-detail.tsx b/App/components/po/po-detail.tsx
index 0982e34..af6ada0 100644
--- a/App/components/po/po-detail.tsx
+++ b/App/components/po/po-detail.tsx
@@ -10,6 +10,7 @@ import { generateDownloadUrl } from "@/lib/storage";
 import { groupAttachments } from "@/lib/attachments";
 import { TC_FIXED_LINE } from "@/lib/validations/po";
 import { parsePoTerms } from "@/lib/terms";
+import { actionLabel } from "@/lib/po-activity";
 import type { LineItemInput } from "@/lib/validations/po";
 import type { Role } from "@prisma/client";
 
@@ -87,26 +88,6 @@ interface Props {
   vendorEmail?: string | null;
 }
 
-const ACTION_LABELS: Record<string, string> = {
-  CREATED: "Created",
-  SUBMITTED: "Submitted for review",
-  APPROVED: "Approved",
-  APPROVED_WITH_NOTE: "Approved with note",
-  REJECTED: "Rejected",
-  EDITS_REQUESTED: "Edits requested",
-  VENDOR_ID_REQUESTED: "Vendor ID requested",
-  VENDOR_ID_PROVIDED: "Vendor ID provided",
-  PAYMENT_SENT: "Payment confirmed",
-  PARTIAL_PAYMENT_CONFIRMED: "Partial payment confirmed",
-  RECEIPT_CONFIRMED: "Receipt confirmed",
-  PARTIAL_RECEIPT_CONFIRMED: "Partial receipt confirmed",
-  CLOSED: "Closed",
-  MANAGER_LINE_EDIT: "Manager amended line items",
-  PRODUCT_PRICE_UPDATED: "Product prices updated",
-  CANCELLED: "Cancelled",
-  SUPERSEDED: "Superseded",
-};
-
 export async function PoDetail({ po, currentUserId, currentRole, readOnly = false, vendorEmail = null }: Props) {
   const lineItemsForEditor = po.lineItems.map((li) => ({
     name: li.name,
@@ -577,7 +558,7 @@ export async function PoDetail({ po, currentUserId, currentRole, readOnly = fals
               <div className="absolute -left-1.5 mt-1.5 h-3 w-3 rounded-full border-2 border-white bg-neutral-400" />
               <div className="flex items-baseline gap-2">
                 <span className="text-sm font-medium text-neutral-900">
-                  {ACTION_LABELS[action.actionType] ?? action.actionType}
+                  {actionLabel(action, po.currency)}
                 </span>
                 <span className="text-xs text-neutral-400">by {action.actor.name}</span>
                 <span className="text-xs text-neutral-400 ml-auto">{formatDateTime(action.createdAt)}</span>
diff --git a/App/lib/po-activity.ts b/App/lib/po-activity.ts
new file mode 100644
index 0000000..490d274
--- /dev/null
+++ b/App/lib/po-activity.ts
@@ -0,0 +1,40 @@
+import type { Prisma } from "@prisma/client";
+import { formatCurrency } from "@/lib/utils";
+
+// Human-readable labels for each POAction type, shown in the PO Activity timeline.
+export const ACTION_LABELS: Record<string, string> = {
+  CREATED: "Created",
+  SUBMITTED: "Submitted for review",
+  APPROVED: "Approved",
+  APPROVED_WITH_NOTE: "Approved with note",
+  REJECTED: "Rejected",
+  EDITS_REQUESTED: "Edits requested",
+  VENDOR_ID_REQUESTED: "Vendor ID requested",
+  VENDOR_ID_PROVIDED: "Vendor ID provided",
+  PAYMENT_SENT: "Payment confirmed",
+  PARTIAL_PAYMENT_CONFIRMED: "Partial payment confirmed",
+  RECEIPT_CONFIRMED: "Receipt confirmed",
+  PARTIAL_RECEIPT_CONFIRMED: "Partial receipt confirmed",
+  CLOSED: "Closed",
+  MANAGER_LINE_EDIT: "Manager amended line items",
+  PRODUCT_PRICE_UPDATED: "Product prices updated",
+  CANCELLED: "Cancelled",
+  SUPERSEDED: "Superseded",
+};
+
+// Produce the Activity-timeline label for an action. Most actions use the static
+// ACTION_LABELS map; PARTIAL_PAYMENT_CONFIRMED interpolates the instalment amount
+// from the action's metadata (already persisted by markPaid) — issue #140.
+export function actionLabel(
+  action: { actionType: string; metadata: Prisma.JsonValue },
+  currency: string,
+): string {
+  const fallback = ACTION_LABELS[action.actionType] ?? action.actionType;
+  if (action.actionType === "PARTIAL_PAYMENT_CONFIRMED") {
+    const amount = (action.metadata as { paymentAmount?: unknown } | null)?.paymentAmount;
+    if (typeof amount === "number" && Number.isFinite(amount)) {
+      return `Partial payment of ${formatCurrency(amount, currency)} confirmed`;
+    }
+  }
+  return fallback;
+}
diff --git a/App/tests/unit/po-activity-label.test.ts b/App/tests/unit/po-activity-label.test.ts
new file mode 100644
index 0000000..ca8e19a
--- /dev/null
+++ b/App/tests/unit/po-activity-label.test.ts
@@ -0,0 +1,54 @@
+import { describe, it, expect } from "vitest";
+import { actionLabel } from "@/lib/po-activity";
+import { formatCurrency } from "@/lib/utils";
+
+describe("actionLabel (Activity timeline)", () => {
+  it("interpolates the instalment amount for a partial payment (issue #140)", () => {
+    const label = actionLabel(
+      { actionType: "PARTIAL_PAYMENT_CONFIRMED", metadata: { paymentAmount: 5000 } },
+      "INR"
+    );
+    expect(label).toBe(`Partial payment of ${formatCurrency(5000, "INR")} confirmed`);
+    expect(label).toContain("5,000");
+  });
+
+  it("respects the PO currency", () => {
+    const label = actionLabel(
+      { actionType: "PARTIAL_PAYMENT_CONFIRMED", metadata: { paymentAmount: 1200 } },
+      "USD"
+    );
+    expect(label).toBe(`Partial payment of ${formatCurrency(1200, "USD")} confirmed`);
+  });
+
+  it("falls back to the plain label when paymentAmount is missing (older audit rows)", () => {
+    expect(
+      actionLabel({ actionType: "PARTIAL_PAYMENT_CONFIRMED", metadata: null }, "INR")
+    ).toBe("Partial payment confirmed");
+    expect(
+      actionLabel(
+        { actionType: "PARTIAL_PAYMENT_CONFIRMED", metadata: { paymentRef: "TXN-1" } },
+        "INR"
+      )
+    ).toBe("Partial payment confirmed");
+  });
+
+  it("falls back when paymentAmount is non-numeric, never rendering NaN", () => {
+    const label = actionLabel(
+      { actionType: "PARTIAL_PAYMENT_CONFIRMED", metadata: { paymentAmount: "5000" } },
+      "INR"
+    );
+    expect(label).toBe("Partial payment confirmed");
+    expect(label).not.toContain("NaN");
+  });
+
+  it("leaves other action labels unchanged", () => {
+    expect(
+      actionLabel({ actionType: "PAYMENT_SENT", metadata: { paymentAmount: 5000 } }, "INR")
+    ).toBe("Payment confirmed");
+    expect(actionLabel({ actionType: "APPROVED", metadata: null }, "INR")).toBe("Approved");
+  });
+
+  it("falls back to the raw action type for unknown actions", () => {
+    expect(actionLabel({ actionType: "MYSTERY", metadata: null }, "INR")).toBe("MYSTERY");
+  });
+});