% Percentage Calculator
Percent of, percent change, and X is what % of Y. Runs privately in your browser.
Three questions, three modes
Pick the mode that matches your question. 'Percent of' answers questions like 'what is 15% of 200'. 'Percent change' answers 'going from 80 to 100 is what percentage increase'. 'Is what % of' answers '30 is what percentage of 150'. All three are the same arithmetic wearing different hats, but phrasing the question correctly is where most people slip.
Percentage change deserves special care: it is (new − old) ÷ old × 100, and it is directional. A rise from 100 to 125 is +25%, but falling back from 125 to 100 is −20% — percentages do not symmetrise. Any percentage change needs its starting point stated or the number is meaningless.
The arithmetic behind each mode
Percent of: X% of Y = X ÷ 100 × Y. Percent change: (B − A) ÷ A × 100. 'X is what % of Y': X ÷ Y × 100.
The percentage traps
- Adding percentage changes across periods. +10% then −10% is −1% overall, not zero.
- Reversing the base. 'What % of 200 is 30' and 'what % of 30 is 200' give wildly different answers.
- Applying percentage points wrong: a rise from 5% to 7% is 2 percentage points but a 40% relative increase.
- Forgetting that percent-off sums compound, as covered in the Discount Calculator guide.
A shirt, an electricity bill, a pay rise
A 200 shirt at 15% off: 15 ÷ 100 × 200 = 30 off, paying 170. Your electricity bill went from 80 to 100: (100 − 80) ÷ 80 = 25% up. If 30 of your 150 customers complained, 30 ÷ 150 = 20% complaint rate. Three different questions, three different setups — the mode selector keeps you honest.
Percentage questions
What is 15% of 200?
30. Enter 'of' mode with 15 and 200 — the calculator shows the arithmetic.
How do I calculate percentage increase?
Use change mode: (new − old) ÷ old × 100. Going from 80 to 100 is a 25% increase.
Why does +25% followed by −25% not return to the start?
Because the second percentage applies to a different base. 100 → 125 → 93.75. Percentages compound; they don't cancel.
What is the difference between percentage and percentage points?
Points are absolute (5% → 7% is +2 points); percent is relative (5% → 7% is +40%). Finance and statistics need the distinction.
Can I chain calculations?
Yes — take one result and feed it back in as an input. The three modes cover every step of a multi-stage percentage problem.
Related maths tools
Tip: double-check inputs before relying on results for important decisions.