Percentage calculator

Percent of, what percent, percent change, increase and decrease.

What do you want to work out?

Use a dot or comma for decimals. A comma followed by exactly three digits is read as a thousands separator (1,234 = 1234).

Result

Enter two numbers to see the result.

What this percentage calculator does

Pick one of six questions, type two numbers and get the answer immediately, together with the formula so you can see how it was worked out. The six questions cover almost every everyday percentage problem:

  1. X% of a number: what is 15% of 80? (12)
  2. X is what % of Y: 25 is what percent of 200? (12.5%)
  3. X is Y% of what: 30 is 20% of what number? (150)
  4. % change: from 50 to 75 is a change of 50%.
  5. Increase by %: 150 increased by 20% is 180.
  6. Decrease by %: 150 decreased by 20% is 120.

How to use it

  1. Choose the question that matches your problem. The labels of the two boxes change to tell you what goes where.
  2. Type the two numbers. You can use a dot or a comma for decimals, and a comma followed by exactly three digits is read as a thousands separator.
  3. Read the result sentence, the difference where it applies, and the formula.
  4. Press "Copy result" to paste the whole sentence into a message or document.

Worked examples

  • A discount. A jacket costs 80 and is 15% off. Use "X% of a number": 15% of 80 is 12, so you save 12 and pay 68. Or use "Decrease by %" with 15 and 80 and get 68 directly.
  • A price with tax added. A 19.99 item with 10% tax: "Increase by %" with 10 and 19.99 gives 21.989, about 21.99.
  • Tax already included. A price of 120 includes 20% tax. The 120 is 120% of the original, so use "X is Y% of what" with 120 and 120 to get 100.
  • How much did it grow? Sales went from 1,200 to 1,500. "% change" gives 25%.
  • A share of a total. 18 of 60 people replied. "X is what % of Y" gives 30%.

Mistakes to avoid

  • Percent versus percentage points. Going from 10% to 12% is a rise of 2 percentage points, but a 20% increase in the rate itself.
  • Increase then decrease. A 20% rise followed by a 20% fall does not return to the start: 100 becomes 120, then 96. The second percentage is taken from a different base.
  • Percent change from zero. It is undefined, because you cannot divide by zero. The calculator says so instead of showing a meaningless number.
  • Negative starting values. The change is measured against the size of the starting value, so a move from -50 to -25 is shown as +50%, which means it moved halfway toward zero.

Tips

  • For quick mental maths, 10% is a tenth, 50% is half, and 1% is a hundredth.
  • Results are rounded to remove computer floating-point noise, so 0.1 + 0.2 shows as 0.3.
  • Keep an eye on which number is the "whole". Swapping the two boxes gives a different, equally valid question.

Frequently asked questions

How do I calculate a percentage of a number?

Divide the percentage by 100 and multiply by the number. For example, 15% of 80 is 15 ÷ 100 × 80 = 12. Choose "X% of a number" and the calculator does it for you.

How do I calculate percentage change?

Subtract the old value from the new one, divide by the old value, and multiply by 100. From 50 to 75 is (75 − 50) ÷ 50 × 100 = 50%. A negative result means a decrease.

Why is the percent change from zero not shown?

The formula divides by the old value, and dividing by zero has no answer. If you start from zero, describe the change as an amount instead of a percentage.

How do I find the original price before a discount?

If the sale price is 68 after 15% off, the sale price is 85% of the original. Use "X is Y% of what" with 68 and 85 to get 80.

Does the calculator work with decimals and big numbers?

Yes. It accepts decimals and thousands separators and rounds the answer sensibly, so results stay readable.

Are my numbers sent anywhere?

No. The calculation happens in your browser as you type, and nothing is stored or sent.

Updated October 13, 2026 · More in Numbers