Percentage formulas
X% of Y = Y × X ÷ 100. For example, 15% of 80 is 12.
X is what percent of Y = X ÷ Y × 100. For example, 12 is 15% of 80.
Percent change = (new − old) ÷ old × 100. From 80 to 100 is a 25% increase; from 100 to 80 is a 20% decrease.
Why isn’t +20% then −20% back to the start?
Each percentage is taken from a different base. 100 plus 20% is 120, but 20% of 120 is 24, so you land on 96. The same applies to two discounts in a row: 20% off and then another 10% off is 28% off in total, not 30%.
Percent vs percentage points
If an interest rate rises from 2% to 3%, it went up 1 percentage point, but by 50 percent. Use the percent change row to see the relative change.
Is anything sent to a server?
No. Every calculation runs in your browser. Nothing you type here is uploaded or stored anywhere else.