Percentage Calculator
The three percentage problems everyone actually has, each solved live as you type.
Calculated on your device.
Quick mental shortcuts
10% = move the decimal one left. 5% = half of that. 15% = 10% + 5% (the tip trick). 25% = quarter it. 1% = decimal two left, then scale: 7% of 300 is 3 × 7 = 21. And X% of Y always equals Y% of X — 8% of 50 feels hard; 50% of 8 is instantly 4.
Common questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100: 15% of 80 = 80 × 15 ÷ 100 = 12. The first row above does it live.
How do I work out what percent one number is of another?
Divide the part by the whole and multiply by 100: 30 out of 120 = 30 ÷ 120 × 100 = 25%. Second row.
How do I calculate percentage increase or decrease?
(New − old) ÷ old × 100. Going from 50 to 65 is (65−50)÷50×100 = +30%. Decreases come out negative. Third row.
Why is a 50% increase followed by a 50% decrease not back to the start?
Because the decrease applies to the new, larger number: 100 → +50% → 150 → −50% → 75. Percentages compound on the current value — the source of half the percentage confusion in the world.