How to Calculate a Percentage — A Complete Beginner's Guide

A percentage is a way of talking about a part of a whole, where the whole is always 100. The word itself comes from Latin roots meaning “per hundred”, and that idea is the key to every percentage calculation: 25% means 25 out of every 100, 50% means half, and 100% means the whole thing. Once you see percentages this way, the formulas stop feeling like magic and start feeling like ordinary arithmetic with a fixed scale.

The basic formula

To find a percentage of a number, multiply the number by the percentage and divide by 100. For example, 20% of 250 is 250 × 20 ÷ 100 = 50. Another way to think about it is to find 1% first and then scale up: 1% of 250 is 2.5, so 20% is 20 × 2.5 = 50. Both routes give the same answer, and the second route is often easier in your head, because 10% is just the number divided by 10, and 5% is half of 10%. If you need 15%, add 10% and 5% together. For 15% of 200, that is 20 + 10 = 30, with no calculator needed.

To find what percentage one number is of another, divide the first number by the second and multiply by 100. If you scored 36 out of 45 in a test, the calculation is 36 ÷ 45 × 100 = 80%. That tells you your share of the total, on a scale where 100% would be a perfect score. The same idea works for savings, survey results and progress towards a goal: if you have saved 150 towards a 500 target, you are 150 ÷ 500 × 100 = 30% of the way there.

Percentage increase and decrease

Percentage change compares a new value with an old value. First find the difference, then divide by the old value, then multiply by 100. If a price rises from 40 to 50, the difference is 10, and 10 ÷ 40 × 100 = 25%, so the price rose by 25%. If a price falls from 50 to 40, the difference is still 10, but the base is now 50, so the fall is 10 ÷ 50 × 100 = 20%. Notice that the same 10 change gives a different percentage depending on where you start, which is why the base always matters and should be stated clearly.

A common trap is adding percentages that have different bases. A shop price that rises by 20% and then falls by 20% does not return to its original price. Start with 100: after a 20% rise it is 120, and a 20% fall from 120 removes 24, leaving 96. The two percentages look equal, but the second one is taken from a larger number, so it has a bigger effect. The same trap appears with pay rises, investment returns and population changes, so always ask: percentage of what?

Percentage points are different

When a percentage itself changes, the difference is measured in percentage points, not percent. If interest rises from 3% to 5%, it has risen by 2 percentage points. In relative terms, though, it has risen by about 67%, because 2 ÷ 3 × 100 is about 67%. News reports often use percentage points for exactly this reason: they avoid exaggerating a small change in a rate. If you read that unemployment rose by 1 percentage point, that is a clear, absolute change; if you read that it rose by 20%, you need to know the starting rate to judge how big that really is.

Percentages in everyday life

Shopping is the most common place to meet percentages. A 30% discount on 90 means a saving of 27 and a final price of 63, which you can check with our Discount Calculator. Tips, tax and interest are the same idea in different clothes: a 15% tip on a 40 meal is 6, and 20% tax on 250 is 50. In school and work, percentages turn raw numbers into comparable ones: a score of 18 out of 20 and a score of 85 out of 100 look different, but as percentages they are 90% and 85%, so the first is better. In health and fitness, body fat percentage, or the percentage of a daily target reached, works the same way, always as a part of a stated whole.

Worked examples to practise

Try these by hand, then check with the calculator. First, 12% of 450: 450 × 12 ÷ 100 = 54. Second, what percentage is 27 of 90? 27 ÷ 90 × 100 = 30%. Third, a salary rises from 2,000 to 2,200: the increase is 200, and 200 ÷ 2,000 × 100 = 10%. Fourth, a phone battery falls from 80% to 20%: it has fallen by 60 percentage points, and it has used three quarters of the charge it had at 80%. Practising with round numbers first builds confidence, and then the same steps work with awkward numbers too.

Rounding and sense-checking

Percentages do not always come out whole. If you get 33.333…%, rounding to 33.3% or 33% is usually fine, but say how you rounded if the exact figure matters, for example in money. Always sense-check: a percentage of a positive number cannot be negative unless you are talking about a change, and a share of a whole cannot exceed 100% unless the part is genuinely larger than the whole you chose. If an answer looks impossible, the most likely cause is the wrong base, a misplaced decimal, or a number typed incorrectly, so redo the step slowly rather than trusting the first result.

The best habit is to translate every percentage problem into plain words before calculating: what is the whole, what is the part, and are we finding a share, an amount, or a change? Answer those three questions and the formula chooses itself. With that habit, percentages become one of the most useful everyday maths skills, because they let you compare, judge deals, track progress and spot misleading claims, all with a single, consistent scale.

Try it yourself

Use the related calculator on this site to check your own examples, then try one by hand to make sure the method makes sense.