Percentage Calculator: % Of, Change, Discount

The four percentage calculations

Tab	Question it answers	Formula
% of	What is 15% of 80?	number × percent ÷ 100
What %	12 is what percent of 80?	part ÷ whole × 100
Change	By how much did 80 grow to 92?	(new − old) ÷ old × 100
Discount	What is $100 after 20% off, plus tax?	price × (1 − d) × (1 + tax)

Worked examples

15% of 80 is 12. Add it to get 92, or subtract it to get 68.
12 out of 80 is 15%.
A price that rises from 80 to 92 increased by 15%.
A $100 item at 20% off costs $80. With an extra 10% off it costs $72, which is 28% off in total, not 30%.

Percent change is always measured against the old value, so a 20% rise followed by a 20% fall does not return to the start. For more, read how to calculate percentages.

Frequently asked questions

How do I calculate a percentage of a number?

Multiply the number by the percentage and divide by 100. For 15% of 80: 80 × 15 ÷ 100 = 12.

How do I calculate percent change?

Subtract the old value from the new value, divide by the old value and multiply by 100.

Can I add sales tax to a discount?

Yes. On the Discount tab enter the price, the discount and optionally an extra discount and a tax rate.