About the Percentage Calculator
A percentage is a way of writing a number as a fraction of 100. "Per cent" literally means "per hundred", so 25% means 25 out of every 100. This calculator covers the four questions people ask most often: how much is a percentage of a number, what percentage one number is of another, how much something has gone up or down in percentage terms, and what a number becomes after adding or removing a percentage. Every result updates as you type, and the formula used is shown below so you can check the working yourself.
How to use the Percentage Calculator
- Pick the box that matches your question — for example "What is P% of X?" for a discount or tip.
- Type your numbers. Decimals and negative numbers are allowed.
- Read the answer in the blue result box. It updates instantly, so you can try different values.
- For a price rise or fall, use "Percentage change" and enter the old value first and the new value second.
The formula behind it
Percentage change vs. percentage points
A percentage change compares a new value with an old one. If a savings rate moves from 4% to 5%, it has risen by one percentage point, but by 25% in relative terms, because 1 is a quarter of 4. News reports often mix these up, so it is worth checking which one is meant.
Percentage changes are also not symmetrical. A 50% fall followed by a 50% rise does not bring you back to where you started: 100 falls to 50, and 50 rises only to 75. To undo a fall of P%, you need a rise of P ÷ (100 − P) × 100 percent.
Everyday uses
Percentages appear in almost every part of daily life. Common examples include:
- Shopping discounts and sale prices (30% off £80).
- Restaurant tips and service charges.
- Sales tax and VAT added to a price.
- Exam marks and test scores.
- Salary rises, inflation and price changes.
- Interest rates on loans and savings.
Examples
Discount
A $80 jacket is 30% off. 30% of 80 = 0.30 × 80 = $24, so you pay 80 − 24 = $56.
Test score
You scored 45 out of 60. 45 ÷ 60 × 100 = 75%.
Price increase
Rent goes from 1,200 to 1,290. (1,290 − 1,200) ÷ 1,200 × 100 = a 7.5% increase.
Adding tax
A $50 item with 8% sales tax: 50 × 1.08 = $54.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 15% of 200 is 0.15 × 200 = 30.
How do I work out a percentage increase?
Subtract the old value from the new value, divide by the old value, and multiply by 100. Going from 80 to 100 is (100 − 80) ÷ 80 × 100 = 25%.
How do I remove a percentage that has already been added?
Divide by (1 + P ÷ 100), not subtract P%. If a price of 120 already includes 20% tax, the price before tax is 120 ÷ 1.20 = 100. Subtracting 20% of 120 would wrongly give 96.
Why can’t I calculate a percentage change from zero?
The formula divides by the starting value, and dividing by zero is undefined. Any rise from zero is technically an infinite percentage increase.
About the author: Ahmed Bilal
Ahmed Bilal is the founder of VolexTool and builds and maintains every calculator on the site. Tax rates and thresholds are taken directly from official sources such as GOV.UK, HMRC, the Canada Revenue Agency and the Australian Taxation Office, the formula is shown on every page, and each update must pass more than 600 automated checks before it goes live. Ahmed is not a tax adviser: for decisions about your own situation, speak to a qualified accountant or financial adviser.