diff --git a/CHANGES.md b/CHANGES.md
index 9c38282..82eacd8 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -1,6 +1,8 @@
 # Changes
 
 ## Unreleased
+- Add discount(items, percent): total after a percentage off, before tax.
+- Tax rate is now 8.25%.
 
 ## 1.2.0
 - total() rounds through roundCents().
diff --git a/src/generated/rates.js b/src/generated/rates.js
index d60b834..f0ffeeb 100644
--- a/src/generated/rates.js
+++ b/src/generated/rates.js
@@ -1,2 +1,2 @@
 // Exported from the pricing service.
-export const TAX_RATE = 0.08;
+export const TAX_RATE = 0.0825;
diff --git a/src/lib/cart.js b/src/lib/cart.js
index 385fd69..332f9ce 100644
--- a/src/lib/cart.js
+++ b/src/lib/cart.js
@@ -8,3 +8,7 @@ export function subtotal(items) {
 export function total(items) {
   return roundCents(subtotal(items) * (1 + TAX_RATE));
 }
+
+export function discount(items, percent) {
+  return roundCents(subtotal(items) * (1 - percent / 100) * (1 + TAX_RATE));
+}
diff --git a/tests/lib/cart.test.js b/tests/lib/cart.test.js
index 7a9eab3..d54b54f 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 { subtotal, total, discount } from '../../src/lib/cart.js';
 
 const items = [{ price: 10, qty: 2 }, { price: 5, qty: 1 }];
 
@@ -9,5 +9,9 @@ test('subtotal adds price times quantity', () => {
 });
 
 test('total applies tax and rounds to cents', () => {
-  assert.equal(total(items), 27);
+  assert.equal(total(items), 27.06);
+});
+
+test('discount takes percent off before tax', () => {
+  assert.equal(discount(items, 10), 24.36);
 });