diff --git a/CHANGES.md b/CHANGES.md
index 9c38282..514a822 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,6 +1,7 @@
 # Changes
 
 ## Unreleased
+- Added discount(items, percent), which returns the total after a percentage discount applied before tax.
 
 ## 1.2.0
 - total() rounds through roundCents().
diff --git a/src/lib/cart.js b/src/lib/cart.js
index 385fd69..4001afa 100644
--- a/src/lib/cart.js
+++ b/src/lib/cart.js
@@ -8,3 +8,9 @@ export function subtotal(items) {
 export function total(items) {
   return roundCents(subtotal(items) * (1 + TAX_RATE));
 }
+
+/** Returns the cart total in dollars after taking percent off the subtotal, before tax. */
+export function discount(items, percent) {
+  const discounted = subtotal(items) * (1 - percent / 100);
+  return roundCents(discounted * (1 + TAX_RATE));
+}
diff --git a/tests/lib/cart.test.js b/tests/lib/cart.test.js
index 7a9eab3..bae87fa 100644
--- a/tests/lib/cart.test.js
+++ b/tests/lib/cart.test.js
@@ -1,6 +1,6 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
-import { subtotal, total } from '../../src/lib/cart.js';
+import { discount, subtotal, total } from '../../src/lib/cart.js';
 
 const items = [{ price: 10, qty: 2 }, { price: 5, qty: 1 }];
 
@@ -11,3 +11,15 @@ test('subtotal adds price times quantity', () => {
 test('total applies tax and rounds to cents', () => {
   assert.equal(total(items), 27);
 });
+
+test('discount takes the percentage off before tax is applied', () => {
+  assert.equal(discount(items, 10), 24.3);
+});
+
+test('discount of zero percent equals the plain total', () => {
+  assert.equal(discount(items, 0), total(items));
+});
+
+test('discount of an empty cart is zero', () => {
+  assert.equal(discount([], 10), 0);
+});