Percentage of a number
Convert the percentage to a decimal and multiply it by the whole.
amount = (percentage / 100) × whole
Example: 20% of 80 = 0.20 × 80 = 16.
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What do you want to calculate?
Calculate a percentage of a number
For example, what is 20% of 80?
%
Use a decimal point. Commas separate thousands: 1,250.50.
Enter both values and the result will appear automatically.
Results display up to 6 decimal places; percentages and percentage points up to 4. Very small nonzero values use scientific notation, for example 1 × 10⁻⁷ = 0.0000001.
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How do you calculate percentages?
A percentage expresses a part per hundred. First identify the whole, the part, and whether the percentage is known or is the value you need to find.
What does one percent mean?
One percent is one hundredth of a whole: 1% = 1/100 = 0.01. Therefore, 25% means 25 hundredths, or one quarter of the whole.
Part as a percentage of the whole
Divide the part by the whole, then multiply the result by 100.
percentage = (part / whole) × 100
Example: 30 out of 120 = (30 / 120) × 100 = 25%.
Reverse percentage
Find the original whole when you know a percentage and its amount.
whole = amount × 100 / percentage
Example: 30 is 15% of the whole: 30 × 100 / 15 = 200.
Percentage change
Compare the difference with the original value, not the new value.
change = ((new − original) / original) × 100
Example: A change from 80 to 100 is a 25% increase.
Increase or decrease by a percentage
Use 1 + p/100 for an increase and 1 − p/100 for a decrease.
new = original × (1 ± percentage / 100)
Example: 100 decreased by 15% = 100 × 0.85 = 85.
Percentage points
Percentage points are the direct difference between two percentages.
difference in pp = new % − original %
Example: From 10% to 13% is +3 pp, but a relative increase of 30%.
How can I calculate percentages mentally?
Start with 1% or 10%, then use them to work out other percentages. For the number 200:
- 1%: divide by 100 → 200 ÷ 100 = 2.
- 10%: divide by 10 → 200 ÷ 10 = 20.
- 5%: halve 10% → 20 ÷ 2 = 10.
- 20%: double 10% → 20 × 2 = 40.
- 25%: divide by 4 → 200 ÷ 4 = 50.
- 50%: take half → 200 ÷ 2 = 100.
Practical percentage calculation examples
Choose a calculation type and follow a short worked example. Open any example in the calculator to change the input values.
Percentage of a number
What is 15% of 240? Fifteen percent of 240 is 36.
240 × 15 ÷ 100 = 36
One number as a percentage of another
What percentage is 45 of 180? The part, 45, is 25% of the whole, 180.
45 ÷ 180 × 100 = 25%
Finding the whole
If 72 represents 30%, what is 100%? The whole is 240.
72 × 100 ÷ 30 = 240
Percentage change
A value rises from 160 to 200. The difference of 40 is a 25% increase.
(200 − 160) ÷ 160 × 100 = 25%
Increasing a number by a percentage
Increase 250 by 12%. Add 30 to get a new value of 280.
250 × 1.12 = 280
Difference in percentage points
A value changes from 18% to 24%. The difference is +6 percentage points.
24% − 18% = +6 pp
Percentages in everyday life
How much does a discount save you? How much more does your shopping cost, and how close are you to a savings goal? These everyday examples show the calculation and explain the result. Open an example in the calculator to use your own numbers.
Store discounts: how much will you pay?
An item costs $80 and is discounted by 25%. The discount is $20, so the sale price is $60.
$80 × 0.25 = $20; $80 − $20 = $60
Shopping costs: what is the percentage increase?
The same shopping basket used to cost $120 and now costs $138. Compare the $18 difference with the original $120. Your shopping costs have risen by 15%.
(138 − 120) / 120 × 100 = 15%
Test scores: what percentage did you get?
A score of 42 points out of a possible 50 is a result of 84%.
42 / 50 × 100 = 84%
Two discounts in a row: can you add them?
An item costs $100. A 20% discount reduces it to $80. A further 10% discount applies to that $80, saving another $8. You pay $72: the combined discount is 28%, not 30%.
$100 × 0.80 × 0.90 = $72; (100 − 72) ÷ 100 × 100 = 28%
Original price: what did it cost before the discount?
After a 20% discount, an item costs $64. The sale price is 80% of the original, so divide by 0.80 to get $80. Adding 20% to $64 would not restore the original price.
$64 ÷ (1 − 20 / 100) = $64 ÷ 0.80 = $80
Savings goals: how far have you got?
You have saved $350 for a bicycle costing $500. Since 350 is 70% of 500, you have reached 70% of your goal. You still need $150.
350 ÷ 500 × 100 = 70%; $500 − $350 = $150
Common pitfalls
- For percentage change, divide the difference by the original value.
- Use percentage points only when comparing two values that are already percentages.
- Do not add successive discounts. A 20% discount followed by another 10% saves 28% overall, because 0.80 × 0.90 = 0.72.
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Frequently asked questions about percentages
How do I calculate a percentage of a price?
Multiply the price by the percentage and divide by 100. For example, 15% of $60 is $60 × 15 ÷ 100 = $9. For a discount, subtract $9 from the original price: the sale price is $51.
How do I find what percentage one number is of another?
Divide the first number by the second and multiply by 100. For example, 30 out of 120 is 30 ÷ 120 × 100 = 25%. The second number represents the whole and must not be zero.
How do I calculate the original price before a discount?
Divide the sale price by (1 − discount / 100). An item costing $64 after a 20% discount originally cost $64 ÷ 0.80 = $80. In the calculator, choose Reverse percentage and enter 64 as the known amount and 80 as the percentage.
Can a percentage be greater than 100%?
Yes. If the part is larger than the whole you are comparing it with, the percentage exceeds 100%. For example, 150 is 300% of 50. This differs from percentage change: a rise from 50 to 150 is a 200% increase.
How do I calculate 20% of 80?
Divide 20 by 100, then multiply the result by 80. The calculation is 0.20 × 80 = 16.
How do I find the whole from a percentage and an amount?
Multiply the percentage amount by 100 and divide by the percentage. If 30 is 15%, the whole is 30 × 100 / 15 = 200.
What is the difference between percent and percentage points?
Percent describes a share of a whole or a relative change. Percentage points are the direct difference between two percentages. A move from 10% to 13% is +3 percentage points but a relative increase of 30%.
Why do equal percentage increases and decreases not cancel out?
The second change uses the new value as its base. Increasing 100 by 20% gives 120, but decreasing 120 by 20% gives 96.
Can I enter decimals and thousands?
Yes. Use a decimal point and optional commas between groups of three digits: 1250.50 or 1,250.50. The input 1.250 means 1.25, while 1,250 means one thousand two hundred and fifty. A comma cannot be used as a decimal separator.
Why must the original value be positive for percentage change?
A zero starting value would require division by zero, so percentage change is undefined. With a negative starting value, the result can be misleading without context. This mode therefore requires a positive original value.