Percentage Calculator
Solve all three everyday percentage problems in one place: what is X% of a number, what percentage one number is of another, and the percentage change between two values. Pick a mode, enter your numbers, done.
How to use this calculator
- Choose the mode that matches your question.
- Enter X and Y — the hints under each field show what they mean in the selected mode.
- Press Calculate. The result shows the answer and the exact arithmetic used.
- Switch modes anytime — your numbers stay in place.
Formula used
Three formulas, one idea: percent means "per hundred". Converting between the fraction form (0.25) and percent form (25%) is just multiplying or dividing by 100.
Example calculation
What is 25% of 400? → 25 ÷ 100 × 400 = 100.
30 is what percent of 150? → 30 ÷ 150 × 100 = 20%.
Change from 80 to 100? → (100 − 80) ÷ 80 × 100 = 25% increase.
How do percentages work?
A percentage expresses a number as a fraction of 100 — "per cent" literally means "per hundred". That single idea powers discounts, interest rates, exam scores, statistics and tips. The three modes above cover nearly every percentage question you'll meet in daily life.
A useful mental trick: X% of Y always equals Y% of X. So 8% of 50 feels hard, but 50% of 8 is obviously 4 — same answer. And to find 10% of anything, just move the decimal point one place left; build other percentages from there (5% is half of that, 20% is double).
Why use this calculator?
- One tool for all three common percentage questions — no hunting for the right variant.
- See the exact arithmetic behind every answer so you can reproduce it manually.
- Handles negative values and decimals correctly, where mental math usually slips.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100, then multiply by the number. 15% of 200 = 0.15 × 200 = 30. Shortcut: find 10% by moving the decimal (20), then add half of that for 5% (10) — total 30.
How do I work out what percentage one number is of another?
Divide the part by the whole and multiply by 100. If you scored 45 out of 60: 45 ÷ 60 × 100 = 75%.
How is percentage change calculated?
Subtract the old value from the new, divide by the old value, and multiply by 100. From 80 to 100: (100 − 80) ÷ 80 × 100 = 25% increase. Note the divisor is always the starting value.
Why is a 50% loss not undone by a 50% gain?
Because each percentage applies to a different base. Losing 50% of 100 leaves 50; gaining 50% of 50 gives only 75. To recover a 50% loss you need a 100% gain — a key insight in investing.