Percentage Calculator

Per cent means per hundred

That is the entire idea, and everything else follows from it. A percentage is a fraction with 100 underneath, so 15 % is 15/100, which is 0.15.

X% of Y = (X ÷ 100) × Y

"Of" means multiply. That is the whole rule, and it explains the property that surprises people:

The order does not matter

15 % of 80 is the same as 80 % of 15. Both are 12. This is not a coincidence or a trick — multiplication is commutative, and both work out to 0.15 × 80 in some arrangement.

It is genuinely useful for mental arithmetic. 4 % of 75 looks awkward; 75 % of 4 is obviously 3. Swap them whenever the swapped version is easier.

Doing it in your head

• 10 % — move the decimal point one place left.
• 1 % — move it two places.
• 5 % — half of 10 %.
• 20 % — double 10 %.
• 15 % — 10 % plus half of it again.

Most everyday percentages can be built from 10 % and 1 % with addition. 37 % of 60 is three lots of 10 % (18), plus seven lots of 1 % (4.2), which gives 22.2.

Common uses

• Tips and service charges, which is why 15 and 20 are on the buttons above.
• Sale prices, though the discount calculator does the subtraction for you.
• Interest and commission.
• Test scores and marks.

The working, step by step

Questions people ask

How do I calculate a percentage of a number?

Divide the percentage by 100, then multiply. 15 % of 80 is 0.15 × 80 = 12.

Is 15% of 80 the same as 80% of 15?

Yes. Both are 12. Multiplication works in either order, so you can swap them whenever it makes the sum easier.

How do I work out 10% in my head?

Move the decimal point one place to the left. 10 % of 47 is 4.7.

What about an awkward percentage like 37%?

Build it from 10 % and 1 %. Three lots of 10 % plus seven lots of 1 %.

Nothing here is sent anywhere

The arithmetic happens in your browser as you type. The numbers you enter are not transmitted, logged or stored, because the page has no server behind it to receive them.