How to use this calculator
- Pick the question that matches what you want to know. Each box works on its own.
- Type your two numbers. The answer updates as you type, with a sentence explaining it.
- Decimals and negative numbers work, for example 17.5% or a change from −20 to 10.
How each one is calculated
X% of Y = X ÷ 100 × Y
X is what % of Y = X ÷ Y × 100
Change from X to Y = (Y − X) ÷ X × 100
Y plus X% = Y × (1 + X ÷ 100)
Y minus X% = Y × (1 − X ÷ 100)
Worked examples
15% of 80 = 15 ÷ 100 × 80 = 12
30 is what % of 120 = 30 ÷ 120 × 100 = 25%
50 to 65 = (65 − 50) ÷ 50 × 100 = +30%
80 to 60 = (60 − 80) ÷ 80 × 100 = −25%
200 plus 15% = 200 × 1.15 = 230
200 minus 15% = 200 × 0.85 = 170
A common trap: up then down
Adding a percentage and then taking the same percentage off does not get you back where you started. 200 plus 15% is 230, but 230 minus 15% is 195.50, because the second 15% is worked out on a bigger number. To undo a 15% rise, divide by 1.15 instead: 230 ÷ 1.15 = 200.
Frequently asked questions
What's the difference between percent and percentage points?
If an interest rate goes from 4% to 5%, it has risen by 1 percentage point, but by 25% (because 1 is a quarter of 4). Use the "percentage change" box for the second kind.
Why can't I work out a change from 0?
A percentage change divides by the starting number, and you can't divide by 0. Any rise from nothing is an infinite percentage, so it's clearer to give the actual difference instead.
How do I remove sales tax or VAT from a price?
Divide by 1 plus the rate, as in the trap above. For the UK, our VAT calculator does this for you with the official rates.