Percentage calculator
The five everyday percentage calculations, with the working shown.
Work out what X% of a value is, what percentage a part represents of a total, the change between two numbers, an increase or discount, and the reverse (X is Y% of what). Each mode shows the result and the working, so you can check it and learn the method.
How to use
- Pick the calculation type: X% of Y, X is what % of Y, change, increase/decrease or the reverse.
- Type the two values in the fields that appear.
- The result shows instantly, along with the written working.
What is X% of a value
The most common calculation: value × percentage ÷ 100. For 15% of 240: 240 × 15 ÷ 100 = 36. Useful for tips, commissions, deposits and checking whether an advertised discount is real.
A handy shortcut: 10% is moving the decimal one place left, and 5% is half of that. With those two you can build almost any percentage in your head.
Finding the percentage between two numbers
With a part and a total, divide the part by the total and multiply by 100 — that is how you get a test score or an expense’s share of a budget.
Percentage change is a different calculation: (new − old) ÷ old × 100. It is the right one for rent adjustments, pay rises and investment returns.
The trap of stacked percentages
A 20% discount followed by a 20% increase does not return the original value, because the second percentage applies to a different base: 100 → 80 → 96. Likewise, two 10% discounts make 19%, not 20%.
To stack percentages, multiply the factors: 1.10 × 1.10 = 1.21. For money growing over time, the compound interest calculator does that month by month.
Frequently asked questions
How do I calculate 10% of a value?
Divide by 10 — or, in general, multiply by the percentage and divide by 100. For 10% of 250: 250 × 10 ÷ 100 = 25. That is exactly what the first mode does.
How do I find what percentage one number is of another?
Divide the part by the total and multiply by 100. If you got 25 out of 200 questions right: 25 ÷ 200 × 100 = 12.5%. Use the "X is what % of Y" mode.
How do I apply an increase or a discount?
For a 10% increase, multiply by 1.10; for a 10% discount, multiply by 0.90. The increase/decrease mode shows both at once, plus the difference.
Why doesn’t −20% then +20% return the original value?
Because the second percentage applies to a smaller base. 100 minus 20% is 80; 80 plus 20% is 96, not 100. Use the change mode to see the real difference between two values.