Percentage Calculator

How to use the percentage calculator

This calculator covers four of the most common percentage questions people search for, organised as tabs so you can jump straight to the one you need: finding what a percentage of a number is, working out what percentage one number is of another, calculating the percentage change between two numbers, and adding or subtracting a percentage from a value (useful for discounts, mark-ups, tips and price rises).

Percentages come up constantly in everyday life — discounts while shopping, interest rates on savings and loans, exam results, pay rises, and comparing statistics in the news. Getting comfortable with how each type of percentage calculation works makes all of these much easier to sanity-check yourself, rather than just trusting a headline figure.

The four modes explained

1. X% of Y

This answers “what is 20% of 150?” — multiply the number by the percentage, then divide by 100. So 20% of £150 is (20 ÷ 100) × 150 = £30.

2. X is what % of Y

This answers “30 is what percentage of 150?” — divide X by Y, then multiply by 100. So 30 ÷ 150 × 100 = 20%.

3. Percentage change from X to Y

This answers “what's the percentage increase or decrease from 80 to 100?” — subtract the original from the new value, divide by the original, then multiply by 100. So (100 − 80) ÷ 80 × 100 = 25% increase.

4. Add or subtract a percentage

This answers “what is 150 plus 20%?” or “what is 150 minus 20%?” — multiply the value by (1 + the percentage as a decimal) to increase, or (1 − the percentage as a decimal) to decrease. So £150 plus 20% is 150 × 1.20 = £180, and £150 minus 20% is 150 × 0.80 = £120.

Worked example: a shopping discount

A jacket is priced at £85 and is reduced by 30% in a sale. Using the “subtract %” mode: 85 × (1 − 0.30) = 85 × 0.70 = £59.50. If you later see the same jacket back at full price and want to know the percentage increase from the sale price, that's the “percentage change” mode: (85 − 59.50) ÷ 59.50 × 100 = roughly 42.9% — noticeably higher than the original 30% discount, because the base amount changed.

A common trap: percentage points vs percentage change

One of the easiest percentage mistakes to make is confusing a change in percentage points with a percentage change. If a savings account's interest rate moves from 4% to 5%, that's a rise of 1 percentage point — but expressed as a percentage change, it's actually a 25% increase in the interest rate itself (1 ÷ 4 × 100 = 25%). Both statements are technically correct, but they tell very different stories, which is why it's worth being precise about which one you mean, especially when reading financial or statistical reporting.

Where percentages show up in real UK life

Beyond the maths classroom, percentages are baked into almost every financial decision — mortgage interest rates, credit card APRs, VAT at the till, pay rise negotiations, exam grade boundaries, and investment returns are all expressed as percentages. Being able to quickly check a percentage calculation yourself, ​ rather than relying on a headline figure, is a genuinely useful everyday skill.

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If you're working out a pay rise or salary change, our take-home pay calculator shows the full effect after tax and deductions, not just the gross percentage increase.