Every kind of percentage, one place
This calculator handles the three percentage questions people actually ask: how much a percentage of a number is, what proportion one number is of another, and how much something changed in percentage terms. Type into any field and the answer updates instantly — no equals button, no page reload.
The formulas behind it
- Percent of a number: (percent ÷ 100) × number. So 20% of 150 = 30.
- What percent of: (part ÷ whole) × 100. So 30 of 150 = 20%.
- Percentage change: ((new − old) ÷ old) × 100. A move from 150 to 180 is a +20% change; from 180 to 150 is −16.7%.
Everyday uses
Percentages show up everywhere: working out a tip or sales tax, checking a discount, reading a test score, comparing price changes, or tracking growth. Having the right formula applied automatically removes the guesswork — and the mental math.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 20% of 150 is 0.20 × 150 = 30.
How do I work out what percent one number is of another?
Divide the part by the whole and multiply by 100. For example, 30 out of 150 is 30 ÷ 150 × 100 = 20%.
How is percentage increase or decrease calculated?
Subtract the old value from the new value, divide by the old value, and multiply by 100. A rise from 150 to 180 is (180 − 150) ÷ 150 × 100 = 20% increase.