How to use it
- Pick the row that matches your question, for example "What is X% of Y?".
- Type the two numbers. The answer updates as you type.
- Read the working underneath to see exactly how the answer was calculated.
- Use the last two rows to add or remove a percentage, such as a discount, tip or sales tax.
Percentage formulas
| Question | Formula | Example |
|---|---|---|
| What is P% of X? | P ÷ 100 × X | 15% of 80 = 12 |
| X is what % of Y? | X ÷ Y × 100 | 30 of 120 = 25% |
| % change from A to B | (B − A) ÷ |A| × 100 | 80 → 100 = +25% |
| X is P% of what? | X ÷ (P ÷ 100) | 45 is 30% of 150 |
| Original before +P% | X ÷ (1 + P ÷ 100) | 120 after +20% = 100 |
Common mistakes
- Reversing a percentage by subtracting it. A price of 120 that includes a 20% increase was 100 before, not 96. Divide by 1.20 instead of taking 20% off.
- Mixing up percent and percentage points. An interest rate rising from 4% to 5% is a rise of 1 percentage point, but a 25% increase in the rate.
- Adding percentage changes. A 10% rise followed by another 10% rise is 21% in total, because the second 10% applies to the larger number.
Everyday uses
Use the first row for tips and discounts, the change row for price rises, salary increases and exam score improvements, and the reverse row to remove sales tax or VAT from a price. For money that grows by a percentage every year, use the compound interest calculator.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 20% of 250 = 20 ÷ 100 × 250 = 50.
How do I calculate percentage increase?
Subtract the original value from the new value, divide by the original value and multiply by 100. From 80 to 100 is (100 − 80) ÷ 80 × 100 = 25% increase.
What is a reverse percentage?
It finds the original number before a percentage was added or taken off. If a price is 120 after a 20% increase, the original was 120 ÷ 1.20 = 100, not 120 − 20% = 96.
Why is a 50% increase followed by a 50% decrease not the same number?
Because each percentage is taken of a different starting value. 100 + 50% = 150, but 150 − 50% = 75.
How do I remove sales tax or VAT from a price?
Use the "original before a % increase" row: enter the price including tax and the tax rate. For example, 120 including 20% tax = 120 ÷ 1.20 = 100 before tax.
Last updated · Built and checked by Moeed Hussain