Percentage calculator

How to use this calculator

Choose the question before entering numbers. Percentage of an amount multiplies the base by the percentage divided by 100. Part as a percentage divides the part by the whole and multiplies by 100. Percentage change compares a new value with a positive original value. Discount subtracts a percentage of the original price.

Worked examples

All numbers here are illustrative. For 20% of 80, enter 80 and 20: 80 × 20 ÷ 100 = 16. A part of 16 out of 80 is 20%. A change from 80 to 100 is (100 − 80) ÷ 80 × 100 = 25%. A 20% discount on 80 leaves 80 × 0.8 = 64, before any taxes or other charges.

Assumptions and limits

The calculator is unit-neutral: amounts may be dollars, items, or another consistent quantity. It does not fetch prices, fees, sales-tax rates, or investment returns. Change mode requires a positive original value; a zero base has no defined relative change. Discount mode accepts 0–100%. For rates changing from 20% to 25%, the difference is 5 percentage points, while the relative increase is 25%.

Check the result

Ask what represents 100%. A discount and an equal percentage increase do not cancel: 80 after 20% off is 64, and 20% added to 64 gives 76.8. Keep full precision until your final reporting step. See the linked guides for reverse percentages, successive discounts, and weighted averages.