Three useful calculations

Percentage of: 15% of 240 is 36.
What percent: 30 is 12.5% of 240.
Percentage change: 80 to 100 is a 25% increase.

The formulas

To find a percentage of a value, multiply the value by the percentage divided by 100. To find a ratio as a percentage, divide the part by the whole and multiply by 100.

Percentage change

Change is calculated as (new − original) ÷ original × 100. A positive answer is an increase and a negative answer is a decrease. Change from zero is undefined.

Rounding

The calculator keeps useful decimal precision while avoiding long floating-point tails. For accounting, tax or regulated decisions, apply the rounding rules required by the relevant authority.