How do I calculate a percentage of a number?

Divide the percentage by 100 and multiply. 15% of 80 = 0.15 × 80 = 12.

How do I work out what percent one number is of another?

Divide the part by the whole and multiply by 100. 30 out of 120 is 30 ÷ 120 × 100 = 25%.

How do I find the whole when I know a part and its percentage?

Divide the part by the percentage as a decimal. If 20 is 40% of something, it is 20 ÷ 0.4 = 50.

What's the difference between percentage points and percent?

If a rate moves from 10% to 12%, that's a 2 percentage point increase but a 20% relative increase — this calculator's 'percent change' mode gives you the relative figure.

Why is 50% off then 50% off not the same as free?

Because each discount applies to the already-reduced price. Two successive 50% discounts leave you paying 25% of the original, not 0%.

How do I calculate a percentage in Excel or Google Sheets?

For X% of Y, use =Y*X/100. For what percent X is of Y, use =X/Y and format the cell as a percentage. For percent change, use =(new-old)/old. They are the same sums this page shows in its working line.

How do I work out 15% in my head?

Find 10% by moving the decimal point one place left, halve that for 5%, and add the two. 15% of 64 is 6.4 + 3.2 = 9.6.

Percentage Calculator: X% of Y, What Percent, Percent Change

Find X% of a number, what percent one number is of another, the whole from a part, or the percent change — with the working.

Inputs

What do you want to work out?

-10,000,00010,000,000

Include CalculateEveryday mark

20% of 500

100

Total: 500

20%100 (20%)
Remainder400 (80%)

Working: 20% = 20 ÷ 100 = 0.2; 0.2 × 500 = 100
500 plus 20%: 600
500 minus 20%: 400

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What each Percentage input means

What do you want to work out?: Pick the question: X% of Y (a tip, a discount, a tax), X is what percent of Y (a score, a share), the percent change from X to Y, or X is Y% of what (the price before a discount, the bill before a tip).
X: The first number. In 'X% of Y' it is the percentage, typed as 20 for 20%, not 0.2. In the other modes it is the part, or the starting value of a change.
Y: The second number: the whole, the new value of a change, or the percentage in 'X is Y% of what'.

Percentage formula

X% of Y = X ÷ 100 × Y · X is what % of Y = X ÷ Y × 100 · X is Y% of W: W = X ÷ (Y ÷ 100) · change = (new − old) ÷ |old| × 100

\text{amount} = \frac{p}{100} \times \text{base}

A percent is a number out of 100, so 20% is 20 ÷ 100 = 0.2. OpenStax Prealgebra frames every percent problem as one equation — amount = percent × base — and the four modes here solve it for whichever piece you are missing. Twenty percent of 500 multiplies: 0.2 × 500 = 100. 'What percent is 30 of 120' divides: 30 ÷ 120 = 0.25, so 25%. 'Twenty is 40% of what' divides the other way: 20 ÷ 0.4 = 50. And percent change takes the difference as a share of the starting value. Every result shows its working, and the first mode also gives the number plus and minus that percentage — the sale price, or the total with tax.

Percentage worked example

20% of 500: 20 ÷ 100 = 0.2, and 0.2 × 500 = 100. So 500 plus 20% is 600 and 500 minus 20% is 400. The same equation run backwards says 100 is 20% of 500, and 20 is 40% of 50.

More Percentage examples

A test score of 42 out of 56: 42 ÷ 56 = 0.75, and 0.75 × 100 = 75%.

A 15% tip came to 18 — what was the bill? 18 ÷ 0.15 = 120, and the check line confirms that 15% of 120 is 18.

Sales tax of 8.25% on a 64 purchase: 8.25 ÷ 100 = 0.0825, and 0.0825 × 64 = 5.28, so the total with tax is 69.28.

Where the Percentage calculator can give the wrong answer

"X is what percent of Y" is undefined when Y is 0, and so is a percent change from 0; the page reports an error rather than infinity.
Percentages above 100 are fine: going from 10 to 50 is a 400% increase, and 150% of 80 is 120.
Adding and then removing the same percentage does not get you back: 100 + 20% is 120, but 120 − 20% is 96.
Percent change divides by the starting value's size, so a move from −50 to −25 reads as an increase.

Spotted a mistake? Tell us

Percentage reference table

Percent, decimal and fraction equivalents, and each percentage of 80
Percent	Decimal	Fraction	That percent of 80
1%	0.01	1/100	0.8
5%	0.05	1/20	4
10%	0.1	1/10	8
12.5%	0.125	1/8	10
15%	0.15	3/20	12
20%	0.2	1/5	16
25%	0.25	1/4	20
33⅓%	0.333…	1/3	26.67
50%	0.5	1/2	40
75%	0.75	3/4	60
100%	1	1	80
150%	1.5	3/2	120

Source: Arithmetic: percent ÷ 100 gives the decimal (OpenStax Prealgebra 2e, §6.1 'Understand Percent')

Percentage FAQ

: Divide the percentage by 100 and multiply. 15% of 80 = 0.15 × 80 = 12.
: Divide the part by the whole and multiply by 100. 30 out of 120 is 30 ÷ 120 × 100 = 25%.
: Divide the part by the percentage as a decimal. If 20 is 40% of something, it is 20 ÷ 0.4 = 50.
: If a rate moves from 10% to 12%, that's a 2 percentage point increase but a 20% relative increase — this calculator's 'percent change' mode gives you the relative figure.
: Because each discount applies to the already-reduced price. Two successive 50% discounts leave you paying 25% of the original, not 0%.
: For X% of Y, use =Y*X/100. For what percent X is of Y, use =X/Y and format the cell as a percentage. For percent change, use =(new-old)/old. They are the same sums this page shows in its working line.
: Find 10% by moving the decimal point one place left, halve that for 5%, and add the two. 15% of 64 is 6.4 + 3.2 = 9.6.