How to use Percentage Calculator
- 1Find the row that matches your question
- 2Type the numbers into the boxes in that sentence
- 3Read the answer as you type
- 4Check the formula shown under the answer
What Percentage Calculator does
A percentage is a fraction with 100 as the bottom number: 15% means 15 out of every 100. Almost every percentage question is one of four shapes — a percentage of a number, one number as a percentage of another, the change between two numbers, or a number grown or shrunk by a percentage.
Each shape has its own formula, and mixing them up is the usual source of wrong answers. A price that rises 20% and then falls 20% does not return to where it started, for example. This page keeps the four side by side, with the formula printed under every answer so you can see exactly what was calculated.
When to use it
- Discounts and sale prices
- Use the increase/decrease row: a £250 coat with 20% off costs 250 × 0.8 = £200. The same row adds tax or a tip when the percentage is added instead.
- Exam marks and scores
- The 'is what % of' row turns 42 out of 60 into 70% instantly, which is how most marks are reported.
- Price, salary and investment changes
- The percentage change row shows how much a value rose or fell relative to where it began — the figure that matters when comparing growth of different-sized amounts.
Percentage Calculator settings explained
- What is X% of Y
- Multiplies Y by X ÷ 100. 15% of 200 is 30. Use it for tips, commissions, deposits and portions of a total.
- X is what % of Y
- Divides X by Y and multiplies by 100. 30 out of 120 is 25%. Use it for scores, shares and completion rates.
- Percentage change
- The difference between the new and old value, divided by the old value, times 100. From 80 to 100 is a 25% increase; from 100 to 80 is a 20% decrease.
- Increase or decrease by X%
- Multiplies the value by 1 + X ÷ 100 for the increase and 1 − X ÷ 100 for the decrease, and shows both results together.
Limits and what to expect
- Percentage change from zero is undefined, because nothing can be divided by zero; the answer shows a dash.
- Answers are rounded to six decimal places for display.
- The calculator does not reverse a percentage (finding the original price before tax); divide by 1 + rate for that.
Troubleshooting
- A 20% rise then a 20% fall doesn't get back to the start
- The fall is 20% of the bigger number. 100 rises to 120, and 20% of 120 is 24, leaving 96. Percentage changes compound; they do not simply cancel out.
- The percentage change is negative
- A negative result means the value went down. The answer also says 'decrease' so the sign is not missed.
- I need the price before VAT was added
- Divide the total by 1 plus the rate. With 20% VAT, £120 ÷ 1.2 = £100. Taking 20% off £120 gives £96, which is the common mistake.
Your files and your privacy
All four calculations run in your browser as you type. The numbers are never sent to a server or stored, so salary figures and prices stay private.
What to use next
FAQ
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. 15% of 200 is 0.15 × 200 = 30.
How do I work out percentage increase?
Subtract the old value from the new one, divide by the old value and multiply by 100. From 50 to 65 is (65 − 50) ÷ 50 × 100 = 30%.
What is the difference between percent and percentage points?
Percentage points are the plain difference between two percentages. An interest rate going from 4% to 5% rises by 1 percentage point, but by 25 percent.
How do I find what percent one number is of another?
Divide the part by the whole and multiply by 100. 18 of 24 is 18 ÷ 24 × 100 = 75%.
Can percentages be over 100?
Yes. A value that more than doubles has risen by over 100%, and 300 is 150% of 200.