What a percentage means
"Percent" means "per hundred." 25% is 25 out of every 100, the same as the fraction 25/100 or the decimal 0.25. Percentages let you compare things of different sizes on one scale: a $12 saving on a $40 shirt (30%) is a better deal than a $15 saving on a $100 jacket (15%), even though $15 is more money.
Almost every percentage problem is one of three questions. The calculators above handle each one.
How to find X% of a number
Turn the percentage into a decimal by dividing it by 100, then multiply.
result = (X ÷ 100) × Y
Example: a 15% tip on a $64 bill.
15 ÷ 100 = 0.15, and 0.15 × 64 = 9.60. The tip is $9.60.
A mental shortcut: 10% of any number is the number with the decimal point moved one place left. 10% of 64 is 6.4. Half of that is 5% (3.2). Add them and you have 15% (9.6).
How to work out what percent one number is of another
Divide the part by the whole, then multiply by 100.
percent = (part ÷ whole) × 100
Example: you scored 45 out of 60 on a test.
45 ÷ 60 = 0.75, and 0.75 × 100 = 75%.
The "whole" must be the total the part belongs to. If 18 of the 24 people at a party had cake, the whole is 24 (everyone at the party), not 18.
How to calculate percentage change
Subtract the old value from the new value, divide by the old value, and multiply by 100. A positive answer is an increase; a negative one is a decrease.
change % = ((new − old) ÷ |old|) × 100
Example: rent went from $1,200 to $1,290 a month.
1,290 − 1,200 = 90. Then 90 ÷ 1,200 = 0.075, and × 100 = 7.5% increase.
Always divide by the starting value. Dividing by the new value is the most common percentage mistake, and it gives a different answer.
Common percentage mistakes
Increases and decreases don't cancel out
If a $100 stock falls 50% to $50, it then needs to rise 100% to get back to $100, not 50%. The second change is measured from a smaller starting number. That's why losses hurt investors more than equal-sized gains help.
Percent vs. percentage points
If an interest rate moves from 4% to 5%, it rose by 1 percentage point but by 25 percent (1 is 25% of 4). News reports often blur these. Use percentage points when comparing two percentages directly.
Reversing a percentage
If a price after a 20% increase is $120, the original was not $96 (120 minus 20%). Divide by 1.20 instead: 120 ÷ 1.2 = $100. The same idea is used to remove sales tax from a total. See our sales tax calculator.
Where percentages show up every day
| Situation | Question type | Try |
|---|---|---|
| Sale price after 30% off | X% of Y | Discount calculator |
| Test score as a percentage | X is what % of Y | Second calculator above |
| How much your salary rose | % change | Third calculator above |
| Interest on savings | X% of Y, repeated | Compound interest |
| Adding VAT to a price | Y + X% of Y | Sales tax calculator |
Frequently asked questions
How do I calculate a percentage on a phone calculator?
To find 18% of 250, type 250 × 18 ÷ 100 = 45. Many phone calculators also have a % key: 250 × 18 % gives 45 directly.
Can a percentage be more than 100%?
Yes. If something grows from 50 to 150, that's a 200% increase. And 150 is 300% of 50. You only can't have more than 100% of a fixed whole, like more than 100% of a pizza.
How do I turn a fraction into a percentage?
Divide the top number by the bottom one and multiply by 100. 3/8 = 0.375 = 37.5%.
Why does percentage change from 0 show no answer?
Percentage change divides by the starting value, and you can't divide by zero. Going from 0 to 10 is a change of +10, but there's no meaningful percentage for it.
Last reviewed November 2026.