Can I multiply by a decimal?

You can pass a decimal like 0.5 to multiply, but it will throw an error if the result isn't an integer.

import { dinero, multiply } from 'dinero.js';
import { USD } from 'dinero.js/currencies';

const d1 = dinero({ amount: 1000, currency: USD }); // $10.00
multiply(d1, 0.5); // Works (1000 * 0.5 = 500)

const d2 = dinero({ amount: 1001, currency: USD }); // $10.01
multiply(d2, 0.5); // Throws (1001 * 0.5 = 500.5)

Dinero.js uses integer arithmetic to avoid floating-point precision issues. When you multiply by a decimal and the result isn't an integer, validation fails.

Using scaled amounts

The safe way to multiply by non-integers is to use a scaled amount. Instead of 0.5, pass { amount: 5, scale: 1 } (5 at scale 1 = 5/10 = 0.5):

import { dinero, multiply, toSnapshot } from 'dinero.js';
import { USD } from 'dinero.js/currencies';

const d = dinero({ amount: 1001, currency: USD }); // $10.01

const result = multiply(d, { amount: 5, scale: 1 }); // $5.005

toSnapshot(result); // { amount: 5005, currency: USD, scale: 3 }

The result's scale increases to preserve precision. This keeps all values as integers throughout the calculation.

TIP

For percentages, the pattern is the same. To calculate 15% of an amount:

multiply(d, { amount: 15, scale: 2 }); // 15 at scale 2 = 0.15

See the Calculating percentages guide for more examples.