diff --git a/use-shopping-cart/core/Entry.js b/use-shopping-cart/core/Entry.js
index cde06ad..047ff9b 100644
--- a/use-shopping-cart/core/Entry.js
+++ b/use-shopping-cart/core/Entry.js
@@ -55,6 +55,7 @@ function Entry({ id, product, quantity, price_metadata, product_metadata }) {
     id,
     quantity,
     value: product.price * quantity,
+    timestamp: new Date().toISOString(), // add a timestamp in ISO 8601 format
     price_data: {
       ...product.price_data,
       ...price_metadata
diff --git a/use-shopping-cart/core/slice.test.js b/use-shopping-cart/core/slice.test.js
index 02fab9f..8065f13 100644
--- a/use-shopping-cart/core/slice.test.js
+++ b/use-shopping-cart/core/slice.test.js
@@ -27,6 +27,7 @@ function mockCartDetails(overrides1, overrides2) {
       formattedValue: '$8.00',
       price_data: {},
       product_data: {},
+      timestamp: new Date().toISOString(),
       ...overrides1
     },
     [`id_efg${counter}`]: {
@@ -41,6 +42,7 @@ function mockCartDetails(overrides1, overrides2) {
       formattedValue: '$10.00',
       price_data: {},
       product_data: {},
+      timestamp: new Date().toISOString(),
       ...overrides2
     }
   }