Percentage Calculator
Enter your figures below and results update automatically. Switch calculation type at any time using the buttons.
Calculation Breakdown
Percentage Calculator UK
Our Percentage Calculator handles the four most common percentage questions in one tool: finding a percentage of a number, working out what percentage one number is of another, calculating a percentage increase or decrease, and increasing or decreasing a number by a percentage. Whether you’re working out a discount, a pay rise, exam marks, or a business growth rate, this calculator gives you an instant, accurate answer.
How to Use the Percentage Calculator
- Choose a calculation type using the buttons at the top: “% of a number”, “X is what % of Y”, “% increase/decrease”, or “Increase/decrease by %”.
- Enter your figures into the fields shown. You can type any number, including decimals and negative values where relevant.
- Use the common percentage presets (5%, 10%, 20%, and so on) for a quick shortcut, or type your own figure.
- Results update automatically as you type, or click Calculate to refresh manually.
- Use Copy Results to copy a plain-text summary, or Print for a printable version.
The Four Percentage Formulas
| Calculation | Formula | Example |
|---|---|---|
| Percentage of a number | Number × (Percentage ÷ 100) | 20% of 150 = 30 |
| X is what % of Y | (X ÷ Y) × 100 | 30 is 20% of 150 |
| Percentage increase/decrease | ((New − Original) ÷ Original) × 100 | 150 to 180 = 20% increase |
| Increase/decrease by % | Number × (1 ± (Percentage ÷ 100)) | 150 increased by 20% = 180 |
Percentage Increase vs Percentage Points
A percentage increase is a relative change measured against the original value, and it is not the same as a change measured in percentage points. For example, if an interest rate moves from 10% to 15%, that is a 5 percentage point increase, but a 50% relative increase, because ((15 − 10) ÷ 10) × 100 = 50%. Our “% increase/decrease” calculation works out the relative percentage change, not the simple percentage-point difference.
Common Everyday Percentage Calculations
- Discounts and sales: Find the sale price by calculating the percentage discount, then subtracting it from the original price.
- Pay rises: Use “increase/decrease by %” to see your new salary after a percentage pay rise.
- Exam marks: Use “X is what % of Y” to convert a raw score, such as 42 out of 60, into a percentage.
- Business growth: Use “% increase/decrease” to compare revenue, customers, or any metric between two periods.
- Tips and service charges: Use “% of a number” to work out a tip amount on a bill.
Important Assumptions
- All calculations use standard percentage arithmetic; there is no rounding applied until the final displayed figures.
- Negative numbers are supported where mathematically valid, which can be useful for figures that can go negative, such as profit and loss.
- The “of this number” field in “X is what % of Y” and the “original value” field in “% increase/decrease” cannot be 0, as dividing by zero is undefined.
- Displayed figures are rounded to 2 decimal places, while intermediate calculations retain full precision.
Frequently Asked Questions
How do I calculate a percentage of a number?
Multiply the number by the percentage, then divide by 100. For example, to find 20% of 150, calculate 150 x 20 / 100, which equals 30.
How do I work out what percentage one number is of another?
Divide the first number by the second number, then multiply by 100. For example, to find what percentage 30 is of 150, calculate (30 / 150) x 100, which equals 20%.
How do I calculate a percentage increase or decrease?
Subtract the original value from the new value, divide by the original value, then multiply by 100. A positive result is an increase and a negative result is a decrease. For example, going from 150 to 180 is a 20% increase.
How do I increase or decrease a number by a percentage?
To increase a number, multiply it by 1 plus the percentage as a decimal. To decrease it, multiply by 1 minus the percentage as a decimal. For example, increasing 150 by 20% is 150 x 1.20 = 180.
What is the difference between a percentage increase and percentage points?
A percentage increase is a relative change, worked out against the original value. Percentage points measure the simple difference between two percentages. Moving from 10% to 15% is a 5 percentage point increase, but a 50% relative increase.
Can I calculate a percentage of a negative number?
Yes. The percentage of a number and X is what % of Y calculators both accept negative numbers, which can be useful for figures such as profit and loss.
Why can’t the of number or original value be 0?
Both of these calculations involve dividing by that number. Dividing by 0 is undefined, so the calculator shows a warning if you enter 0 in those fields.