About the Percentage Calculator
The three percentage problems everyone actually needs: what is X% of Y, X is what percent of Y, and the percent change between two numbers — solved instantly as you type.
Calculations happen as you type, inside your browser. The figures you enter — which are often salary, invoice or medical numbers — are never uploaded or stored.
How to use it
- Choose which of the three percentage questions you are asking.
- Enter your two numbers.
- Read the answer, which updates on every keystroke.
The three questions this actually answers
What is X% of Y? Multiply Y by X and divide by 100. This is the discount, tip and tax case.
X is what percent of Y? Divide X by Y and multiply by 100. This is the score, share and completion case.
What is the percent change from X to Y? Subtract, divide by the original figure, multiply by 100. Dividing by the wrong one is the single most common percentage error there is.
A worked example
All three, with real numbers:
- 15% of 240 = 36
- 45 is 25% of 180
- Going from 80 to 92 is a 15% increase — because 12 ÷ 80 = 0.15, not 12 ÷ 92
That last one catches people constantly. Divide by where you started, never where you ended up.
Common mistakes
- A 20% fall followed by a 20% rise does not return you to the start. £100 → £80 → £96.
- Confusing percent and percentage points. Moving from 4% to 6% is a rise of two percentage points, but a 50% increase.
- Adding percentages of different totals together as if they were the same unit.
Questions people ask
Why doesn't a 50% loss cancel a 50% gain?
Because each percentage is taken from a different base. Halve 100 and you get 50; add 50% of 50 and you only get back to 75. Recovering a 50% loss takes a 100% gain.
How do I remove tax rather than add it?
Divide by 1 plus the rate. To strip 20% tax from 120, calculate 120 ÷ 1.20 = 100. Subtracting 20% would give 96, which is wrong.
What is a percentage point?
The plain arithmetic difference between two percentages. It exists precisely so that 'from 4% to 6%' can be stated without ambiguity.