How to use the Percentage Calculator
- Choose what you want to find: a percentage of a number, what percent one number is of another, or the whole amount.
- Type your two numbers. The answer updates as you type.
- Open “How it was calculated” to see the formula with your numbers filled in.
- Use Copy result to paste the answer into a message or document.
What does this tool do?
Almost every percentage question is one of three shapes. “What is 15% of 80?” asks for a part. “30 is what percent of 120?” asks for a rate. “45 is 30% of what?” asks for the whole. This calculator handles all three, so you don't need to remember which way round to divide.
When you find a percentage of a number, it also shows that number with the percentage added and taken away, which covers quick tax, tip and markup questions.
Why use it?
- No formula to remember — pick the question in plain words.
- Shows every step, which is useful for homework and for checking reports.
- Handles decimals and negative numbers correctly.
Worked examples
Here are the three question types with real numbers:
| Question | Calculation | Answer |
|---|---|---|
| What is 15% of 80? | 15 ÷ 100 × 80 | 12 |
| 30 is what % of 120? | 30 ÷ 120 × 100 | 25% |
| 45 is 30% of what? | 45 ÷ 0.30 | 150 |
The formulas
All three are the same relationship, rearranged. If you know any two of part, rate and whole, you can find the third.
Privacy
The calculation happens instantly in your browser. The numbers you enter are not sent to our servers or saved. There's no account to create and nothing to install.
Frequently asked questions
How do I calculate a percentage of a number in my head?
Find 10% by moving the decimal point one place left, then scale. For 15% of 80: 10% is 8, 5% is half of that (4), so 15% is 12.
Is X% of Y the same as Y% of X?
Yes. 8% of 50 and 50% of 8 are both 4, because multiplication works in either order. Sometimes the swapped version is much easier to work out.
How do I work out a percentage increase between two numbers?
That's a percentage change question. Use the Percentage Change Calculator, which divides the difference by the original value.
Last reviewed by the M2Toolkit team.