Percentage Calculator

Pick a mode to find a percentage of a number, what percent one number is of another, the percentage increase or decrease between two numbers, a number plus or minus a percent, or your marks as a percentage. Every answer shows the formula and one worked line.

Free, no signupNo daily limitRuns in your browser - nothing you enter is uploadedUpdated 7 October 2026

Use this to find a share of an amount: a discount, a tip, a tax, a commission.

What is% of?

Which formula am I using?

Question	Formula	Example
What is X% of Y?	`X × Y ÷ 100`	20% of 150 = 20 × 150 ÷ 100 = 30
X is what % of Y?	`X ÷ Y × 100`	30 ÷ 150 × 100 = 20%
% change from A to B	`(B − A) ÷ \|A\| × 100`	(100 − 80) ÷ 80 × 100 = +25%
Y plus or minus X%	`Y ± Y × X ÷ 100`	200 + 15% = 200 + 30 = 230
Marks percentage	`obtained ÷ total × 100`	375 ÷ 500 × 100 = 75%

Worked example: a price that goes down and back up

A jacket costs 100. It is reduced by 20%, then the sale ends and the price rises by 20%. Is it back to 100?

sale price = 100 − 100 × 20 ÷ 100 = 80 after sale = 80 + 80 × 20 ÷ 100 = 96 to get back = (100 − 80) ÷ 80 × 100 = 25% increase

No - each percentage is taken of a different base. The drop is 20% of 100, the rise only 20% of 80. This is the most common percentage mistake, and the reason the increase/decrease tab always treats the starting value as the base.

Percent, percentage points and the base

A percentage is always "per hundred" of something, and that something - the base - is where most errors come from. In "X% of Y" the base is Y. In a percentage change it is the starting value.

When two percentages are compared, say an interest rate going from 4% to 5%, the difference is 1 percentage point but a 25% increase. Both are correct; they answer different questions.

For marks, the base is the total marks. The grade bands under the marks result are an editable example; boards and schools set their own, so change them to match yours.

Frequently asked questions

How do I calculate a percentage of a number?

Multiply the number by the percentage and divide by 100. 20% of 150 is 20 × 150 / 100 = 30.

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

Divide the part by the whole and multiply by 100. 30 out of 150 is 30 / 150 × 100 = 20%.

How is percentage increase calculated?

Subtract the old value from the new value, divide by the old value and multiply by 100. Going from 80 to 100 is (100 − 80) / 80 × 100 = 25%. A negative answer means a decrease.

Why is a 20% decrease not undone by a 20% increase?

Because each percentage is taken of a different starting number. 100 minus 20% is 80, but 80 plus 20% is only 96. To get back to 100 from 80 you need a 25% increase.

How do I calculate my marks percentage?

Divide the marks you obtained by the total marks and multiply by 100. 375 out of 500 is 375 / 500 × 100 = 75%. The grade bands under the result are examples you can edit to match your school or board.

Why does percentage change from 0 show an error?

Percentage change divides by the starting value. If the starting value is 0 that division is undefined, so there is no meaningful percentage - only the absolute difference.

What this calculator does not do

Percentage change uses the starting value as the base. It is not the symmetric "percentage difference" some science courses use.
The grade bands in marks mode are editable examples, not any board's or school's official scale.
Results are rounded for display to four decimal places; the calculation itself uses full precision.

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Step-by-step guide: How to calculate a percentage →

Built and checked by Taimur Hassan Siddiqui, who has more than ten years in computer-science education. The formulas on this page are covered by an automated test suite, and the worked example on this page is one of its cases. Last updated 7 October 2026.