Percentage Calculator
Pick the question you are asking, enter two numbers and get the answer with the working shown underneath.
Calculated in your browser. Nothing you type is sent anywhere.
- How it works
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- Difference
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- Multiplier
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Percentages in plain words
A percentage is a fraction out of 100. When you say 15%, you mean 15 out of every 100, or 0.15. Nearly every percentage problem is one of six questions, and this calculator has a setting for each one. Choose the question, enter two numbers and read the answer and the working underneath it.
The six formulas
| Question | Formula | Example |
|---|---|---|
| What is X% of Y? | X / 100 x Y | 15% of 200 = 30 |
| X is what percent of Y? | X / Y x 100 | 30 of 200 = 15% |
| Percent change from X to Y | (Y - X) / X x 100 | 80 to 100 = +25% |
| Increase Y by X% | Y x (1 + X / 100) | 200 + 15% = 230 |
| Decrease Y by X% | Y x (1 - X / 100) | 200 - 15% = 170 |
| X is P% of what number? | X / (P / 100) | 30 is 15% of 200 |
Worked example: a price goes up
A monthly subscription rises from $80 to $100.
- Change: $100 - $80 = $20
- Relative to the old price: $20 / $80 = 0.25
- As a percent: 25% increase
If the price then fell back from $100 to $80, that drop is only 20%, because the base is now $100.
Mental math shortcuts
- 10%: move the decimal one place left. 10% of 86 is 8.6.
- 5%: take half of 10%. 5% of 86 is 4.3.
- 1%: move the decimal two places left, then multiply to get other values.
- 15% tip or tax: add 10% and 5%. For 86 that is 8.6 + 4.3 = 12.9.
- 25%: divide by 4. 50%: divide by 2. 75%: three quarters.
Common mistakes
- Mixing up the base. A percent change always uses the starting value as the base, which is why +25% and -20% are opposites.
- Adding percentages. Two 10% discounts in a row are 19% off, not 20%, because the second applies to the reduced price.
- Percent versus percentage points. A rate that moves from 4% to 6% rose 2 points, or 50% in relative terms.
For shopping use the discount calculator, which handles stacked offers and tax. For restaurant bills use the tip calculator.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percent by 100 and multiply by the number. 15% of 200 is 0.15 x 200 = 30.
How do I find percent change?
Subtract the old value from the new one, divide by the old value and multiply by 100. Going from 80 to 100 is (100 - 80) / 80 x 100 = 25% increase.
Why is a 20% increase followed by a 20% decrease not back to the start?
The second percentage applies to a larger number. 100 up 20% is 120, and 20% of 120 is 24, which leaves 96. To undo a 20% rise you need a decrease of about 16.7%.
What is the difference between percent and percentage points?
If a rate rises from 4% to 6%, it rose 2 percentage points, but it increased by 50% in relative terms, because 2 is half of 4.
Can I use negative numbers?
Yes. A negative percent change means a decrease. For the change from zero the percent cannot be calculated, so the calculator tells you instead of showing a wrong number.
Results are estimates for general information. Check important numbers with an official source or a qualified professional. How we calculate and where numbers come from. Last reviewed October 2026.