Percentage Calculator
Work out percentages, ratios and percent change in one place.
Three quick modes: find X% of a number, work out what percent one value is of another, and calculate the percentage change between two values. Clear results as you type, all computed privately in your browser.
Pick the mode that matches your question: use "% of a number" to find a share of an amount (e.g. 15% of a bill), "What percent" to see what fraction one value is of another (e.g. how much 30 is out of 120), and "% change" to measure the increase or decrease between an old value and a new one. Enter the two numbers that mode asks for and the result updates instantly, entirely in your browser.
Common mistakes
- Mixing up "X% of Y" with "X is what percent of Y" — they use different formulas and rarely give the same answer.
- Calculating percentage change as (new − old) ÷ new instead of the correct (new − old) ÷ old; the difference is easy to miss but changes the result, especially when the value has dropped.
- Assuming a percentage decrease and increase cancel out symmetrically — a 50% decrease needs a 100% increase to get back to the original value, not another 50%.
Frequently asked questions
How is percentage change calculated?
Percentage change is (new − old) ÷ old × 100, so a rise from 200 to 250 is +25%.
Why doesn't a 50% increase undo a 50% decrease?
Because each percentage is calculated on a different base. Dropping 200 by 50% gives 100, but increasing 100 by 50% only gives 150 — you'd need a 100% increase to get back to 200.
How do I calculate percentage change when the old value is negative or zero?
The formula (new − old) ÷ old × 100 breaks down when the old value is zero, since dividing by zero is undefined — there is no meaningful percentage change from nothing. With a negative old value the formula still works mathematically, but the sign of the result can be counterintuitive, so it's worth checking the numbers by hand.
What's the difference between percentage points and percent?
If a rate moves from 20% to 25%, that's a change of 5 percentage points, but a 25% increase in the rate itself ((25 − 20) ÷ 20 × 100). The two describe different things and are often mixed up in news headlines.
Which mode do I use to find 15% of a bill?
Use "% of a number": enter 15 as the percentage and the bill total as the value.
Privacy
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