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Percentage Calculator

All the common percent problems in one place. Pick the mode you need, enter your numbers and get the answer.

Last updated: 11 Nov 2026 Read time: 4 min Category: Math Runs locally in your browser
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What a Percentage Is

A percentage is a way of writing a fraction with a fixed denominator of one hundred. The word comes from the Latin per centum, meaning "by the hundred", and the symbol % evolved in Italian merchant manuscripts of the 15th century. Saying that something is 25 percent is the same as saying it is 25 out of every 100, or the fraction 25/100, or the decimal 0.25. Percentages are universal in daily life because they make unlike quantities comparable: a 20 percent raise, a 20 percent exam score, and a 20 percent tip all share the same relative meaning.

To convert in either direction, divide a percent by 100 to get the decimal (so 7.5% becomes 0.075), and multiply a decimal by 100 to get the percent (so 0.42 becomes 42%). Fractions behave the same way: 3/4 = 0.75 = 75%.

The Four Common Problems

Find X% of Y: result = Y x (X / 100). Example: 15% of 200 = 200 x 0.15 = 30.

X is what percent of Y: result = (X / Y) x 100. Example: 50 is (50 / 200) x 100 = 25% of 200.

Percent increase or decrease from X to Y: result = ((Y - X) / X) x 100. Example: 200 to 250 is a (50 / 200) x 100 = 25% increase. 250 to 200 is a (-50 / 250) x 100 = -20% change, i.e. a 20% decrease.

Reverse percentage: if a value after a p% rise is V, the original was V / (1 + p/100). If a price with VAT at 20% is 120, the pre-tax price is 120 / 1.20 = 100.

How to Use This Tool

  1. Pick a mode from the Mode dropdown.
  2. The two labelled fields change meaning depending on the mode you pick. Read them carefully.
  3. Type the first value into the X field.
  4. Type the second value into the Y field.
  5. Click Calculate.
  6. Read the result sentence, which spells out the arithmetic as well as the answer.

Common Use Cases

  • Shopping discounts: work out the sale price when an item is "20% off".
  • Tip calculation: compute a 15 or 18 percent tip on a restaurant bill.
  • Exam grades: convert raw marks to a percentage score.
  • Growth metrics: measure month-over-month or year-over-year change in revenue or users.
  • Tax addition: add sales tax, VAT, or GST to a pre-tax price.
  • Reverse VAT: extract the pre-tax amount from a tax-inclusive total.

Common Mistakes to Avoid

  • Thinking two percent changes add. A 10% rise then a 10% fall is a 1% net loss, not zero.
  • Confusing percent with percentage points. An interest rate going from 4% to 6% is a 2 percentage point rise but a 50% relative rise.
  • Dividing by the new value instead of the old when computing percent change. Always divide by the original.
  • Forgetting that percentage of a negative number is still a percentage of that magnitude; signs matter.
  • Mixing up "X percent more" (multiply by 1.X) with "X percent of" (multiply by 0.X).

Compound Percentages and Everyday Pitfalls

Compound percentages come up more often than people expect. A salary that rises 5% a year for three years ends at 1.05 x 1.05 x 1.05 = 1.1576 times the starting figure, a 15.76% gain, not 15%. The same is true of stacked investment returns, compound inflation, and successive price hikes. Whenever changes stack, multiply the growth factors instead of adding the percentages.

In retail, stacked discounts are the mirror image. A sign that says "extra 10% off already reduced prices" where items were already 20% off yields 0.80 x 0.90 = 0.72, a 28% total discount, not 30%. Shoppers who do the math quickly can judge whether a two-stage offer is as generous as it sounds.

Important For financial decisions involving interest, taxes, or investment returns, remember that percentages compound over time. A simple percentage calculation may not reflect the true outcome over multiple periods. Use a dedicated compound interest tool for long horizons.

Privacy

Your numbers never leave the browser. All arithmetic runs client-side in JavaScript. Nothing is transmitted, stored, or shared.

Frequently Asked Questions

How do I calculate a percentage of a number?

Multiply the number by the percentage expressed as a decimal. For example, 15 percent of 200 equals 200 x 0.15 = 30. Use the "What is X percent of Y" mode of the calculator for an instant answer.

How do I do a reverse percentage?

If you know the result after a percentage change, divide by (1 + percent/100) to go back to the original. If a price rose by 20 percent to 120, the original was 120 / 1.20 = 100. For percent-of problems, divide the part by the percentage to find the whole.

Can I chain or compound percentage changes?

Percentage changes do not simply add. A 10 percent rise followed by a 10 percent fall does not return you to the start: 100 becomes 110, then 99. Multiply the factors instead: 1.10 x 0.90 = 0.99, a net 1 percent loss.

What are typical tipping percentages around the world?

Norms vary. In the United States restaurant tips are typically 18 to 22 percent, in the United Kingdom 10 to 12.5 percent is common and often added as a service charge, in much of Europe rounding up or 5 to 10 percent is enough, and in Japan tipping is not expected.

How do I convert a grade to a percentage?

Divide the marks obtained by the maximum marks possible and multiply by 100. For example, 72 out of 90 is 72 / 90 x 100 = 80 percent. Use the "X is what percent of Y" mode of the calculator.

What is the difference between percent and percentage point?

A percentage point is an absolute arithmetic difference between two percentages. An interest rate rising from 4 percent to 6 percent has risen by 2 percentage points, but by 50 percent in relative terms.

Are my inputs saved?

No. Calculations happen entirely in your browser. Numbers are never sent to a server or saved.