How do I calculate a percentage of a number?

Convert the percentage to a decimal by dividing by 100, then multiply by the number. For 15% of 80 that is 0.15 × 80 = 12.

How do I find what percent one number is of another?

Divide the first number by the second and multiply by 100. 12 out of 80 is 12 ÷ 80 × 100 = 15%.

Can a percentage be more than 100%?

Yes. 150% of a number is one and a half times that number. Values above 100% show up in growth figures and when you compare a total against a smaller reference.

How do I work out the original number from a percentage?

Divide the part by the percentage written as a decimal. If 12 is 15% of a number, the number is 12 ÷ 0.15 = 80.

Percentage Calculator

Find X% of a number, what percent one number is of another, or the total behind a percentage.

Updated September 19, 2026Checked by the editorial team

What is X% of Y?

Percentage

Number

Result

(15 ÷ 100) × 80 = 12

Almost every percentage question is one of three: what is X% of Y, what percent is A of B, or what number has this part as its X%. The calculator below handles all three, updates as you type and shows the arithmetic so you can follow it.

Use it to check a tip, a sales tax figure, a test score or a conversion rate. Nothing you type leaves your browser.

How percentage calculator works

Pick the question you are asking. In the first mode you enter a percentage and a number, and the tool returns that share of the number. In the second you enter two numbers and it returns the first as a percentage of the second. In the third you enter a part and the percentage it represents, and it works back to the whole.

Percent means per hundred, so 15% is 15 out of every 100, or 0.15 as a decimal. Every mode is that one idea rearranged.

The formula

X% of Y  =  (X ÷ 100) × Y
A is what % of B  =  (A ÷ B) × 100
Whole  =  Part ÷ (X ÷ 100)

The three lines are the same relationship solved for a different unknown.

Worked example: a 15% share of 80, and back again

What is 15% of 80? 15 ÷ 100 = 0.15, and 0.15 × 80 = 12.

12 is what percent of 80? 12 ÷ 80 = 0.15, and 0.15 × 100 = 15%.

12 is 15% of what number? 12 ÷ 0.15 = 80.

When to use this tool

Checking a service charge, sales tax or commission before you pay or quote it.
Turning a test score, such as 42 out of 50, into a percentage.
Finding a share of a budget, for example 30% of a monthly income.
Reading survey and analytics numbers: 18 sign-ups from 240 visitors is 7.5%.

Common mistakes to avoid

Dividing by the wrong number. In “A is what % of B” the base is always B, the number after “of”.
Forgetting to divide by 100 and multiplying by 15 instead of 0.15.
Treating percentage points and percent as the same thing. A rate that moves from 4% to 6% has risen 2 percentage points, which is a 50% increase.
Adding and then removing the same percentage and expecting to land where you started. +20% then −20% leaves you 4% below the start.

Frequently asked questions

How do I calculate a percentage of a number?: Convert the percentage to a decimal by dividing by 100, then multiply by the number. For 15% of 80 that is 0.15 × 80 = 12.
How do I find what percent one number is of another?: Divide the first number by the second and multiply by 100. 12 out of 80 is 12 ÷ 80 × 100 = 15%.
Can a percentage be more than 100%?: Yes. 150% of a number is one and a half times that number. Values above 100% show up in growth figures and when you compare a total against a smaller reference.
How do I work out the original number from a percentage?: Divide the part by the percentage written as a decimal. If 12 is 15% of a number, the number is 12 ÷ 0.15 = 80.

Learn more

Results are for information only and are not financial, legal or medical advice. The calculation logic is covered by automated tests, and examples on this page are worked out and re-checked before publishing. Spotted a mistake? Tell us.