Percentage Calculator

Work out a percentage of a value, what share one number is of another, or a value after adding or removing a percentage.

What do you need?

Percentage (%)

Of this number

Result

30.00

Percentage: 15.00%
Of value: 200.00
Result: 30.00

How this is calculated

15.00 ÷ 100 × 200.00

What this tool does

Most percentage work at a desk is one of three questions: what is 15% of this, what share is this of that, or what does this become after adding or removing a percentage. Each is easy to get slightly wrong under time pressure, and the mistakes look plausible.

Every result shows the formula it used, which matters when the number is going into a document someone else will check.

When you might need it

Applying a discount or commission: Work out the amount rather than the resulting price, when the amount is what you need to record.
Reporting a share: Turning "34 of 220 responses" into a percentage for a summary.
Adding a surcharge or removing a deduction: Getting to the figure after a percentage is applied in either direction.
Sanity-checking a spreadsheet: A quick independent check of a number a formula produced.

Common workplace uses

Working out a commission: The payable amount on a sale at an agreed rate.
Summarising survey results: Converting raw counts into the percentages a slide needs.
Applying a discount: Both the discount amount and the resulting price.
Checking a deduction: Confirming a percentage taken off an amount matches what was expected.

How to use it

Pick the question you are asking
The three tabs are: a percentage of a number, X is what percent of Y, and add or remove a percentage.
Enter the two numbers
The labels change to match the mode so it is clear which value goes where.
For the third mode, choose a direction
Add applies the percentage on top; Remove takes it off.
Read the result and the formula
The breakdown below shows each input and the arithmetic used.

Practical tips

Adding then removing the same percentage does not return you to the start: Add 10% to 100 and you get 110. Remove 10% from 110 and you get 99. The percentage applies to a different base each time — this is the single most common percentage error in business.
A percentage of a percentage is not a sum: A 10% discount followed by a further 10% is 19% off, not 20%, because the second applies to the already-reduced price.
Keep the base explicit when you report: "15% higher" is ambiguous without saying higher than what. Write the base into the sentence.
Percentage points are not percent: A rate moving from 5% to 7% is a rise of two percentage points, and also a 40% increase. Both are true and they mean different things.

Common questions

How do I calculate a percentage of a number?

Divide the percentage by 100 and multiply by the number. 15% of 200 is 0.15 × 200 = 30. The first tab does this.

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

Divide the part by the whole and multiply by 100. 30 out of 200 is 15%. The second tab does this, and guards against a total of zero, which has no meaningful percentage.

Why is removing a percentage not the reverse of adding it?

Because each is applied to a different base. Adding 10% to 100 gives 110; removing 10% from 110 removes 11, not 10, leaving 99. To reverse an increase you divide rather than subtract.

Can it handle negative numbers?

Yes. The arithmetic is applied as given, so a negative starting value produces a mathematically correct result — just check it means what you intend in context.

Is my input stored?

No. Everything is calculated in your browser as you type. Nothing is transmitted or saved.