Work Out Any Percentage in Seconds
This percentage calculator handles the three questions people reach for most: finding a percentage of a number, figuring out what percentage one number is of another, and calculating a percentage change between two values. Type your numbers in and the answer appears instantly.
Everything runs in your browser. No data is sent to any server, so you can calculate freely with sensitive figures like salaries, budgets, or exam scores.
How to Use the Percentage Calculator
- Pick a calculation type using the tabs or dropdown above: % of a number, is what %, or % change.
- Enter your numbers into the fields provided.
- Read the result – it updates the moment you finish typing. No button needed.
- Switch between modes at any time; your inputs are not cleared.
Worked Example – Step by Step
Suppose you see a jacket priced at £85 that has a 20% discount. You want to know the sale price.
- Choose the X% of Y mode.
- Enter 20 in the percentage field and 85 in the number field.
- The calculator shows: 20% of 85 = 17.
- Subtract: £85 − £17 = £68 sale price.
Same tool, different question: your team scored 34 out of 40 on a quiz. What percentage is that? Switch to X is what % of Y, enter 34 and 40 – result: 85%.
How It Is Calculated – The Formulas
Three formulas cover almost every everyday percentage problem. Here they are in plain words and as code you can copy into a spreadsheet:
1. Find X% of Y
Divide the percentage by 100, then multiply by the number.
Result = (X / 100) × Y2. X is what percent of Y?
Divide X by Y, then multiply by 100.
Result = (X / Y) × 1003. Percentage change from old to new
Subtract the old value from the new, divide by the old value, multiply by 100. A positive result is an increase; negative is a decrease.
Result = ((New − Old) / Old) × 100Quick-Reference Formula Table
| Question | Formula | Example | Answer |
|---|---|---|---|
| X% of Y | (X ÷ 100) × Y | 15% of 200 | 30 |
| X is what % of Y? | (X ÷ Y) × 100 | 45 is what % of 180? | 25% |
| Percentage increase | ((New − Old) ÷ Old) × 100 | Old: 50, New: 60 | +20% |
| Percentage decrease | ((New − Old) ÷ Old) × 100 | Old: 80, New: 64 | −20% |
Percentage Change vs. Percent Off vs. Percentage Difference – When to Use Each
Percentage change (increase or decrease) compares a new value to an old one over time. Use it for price movements, population growth, or any before-and-after comparison.
Percent off is a shopping shorthand for a percentage decrease applied to a starting price. It uses the same formula – just label the original price as "old" and the discounted price as "new."
Percentage difference is different: it compares two values where neither is the "before" – for example, comparing the populations of two cities. The formula averages the two values as the base instead of using one as the reference. The calculator's % change mode is best when one value is clearly the starting point.
Quick Tips and Common Mistakes
- Forgetting to divide by 100: A very common slip. 20% of 50 is (20 ÷ 100) × 50 = 10, not 20 × 50 = 1,000.
- Mixing up the base: "A 50% increase followed by a 50% decrease" does not get you back to the start. 100 → +50% → 150 → −50% → 75. Always check which number is the base.
- Percentage points ≠ percentage change: If interest rates rise from 2% to 3%, that is a 1 percentage point rise but a 50% increase in the rate itself.
- Rounding too early: If you are doing a multi-step calculation, keep the full decimal until the final answer.
- Negative percentage change is fine: A result of −25% simply means the value fell by a quarter.
Your Privacy
All calculations happen directly in your browser using JavaScript. Nothing you type is uploaded or stored anywhere. You can use this tool with real salary figures, test scores, or financial data without any concern.
Ready to crunch your numbers? Use the percentage calculator at the top of this page – pick your mode, type your values, and get the answer instantly.