Percentage Calculator
A percentage is a fraction out of 100. This calculator handles the five percentage questions people ask most: what is X% of Y, X is what percent of Y, how much did something change in percent, and what is a number after a percent increase or decrease. Pick the question, enter the two numbers, and the result and working appear instantly.
How to use the percentage calculator
- Choose the type of percentage question from the drop-down.
- Enter X and Y. The labels change meaning with the question, so read the result line to confirm you asked what you meant.
- Read the answer in the highlighted row and check the steps underneath to see how it was worked out.
Formula
- X% of Y = X ÷ 100 × Y
- X is what % of Y = X ÷ Y × 100
- % change = (new − old) ÷ |old| × 100
- Increase Y by X% = Y × (1 + X ÷ 100)
- Decrease Y by X% = Y × (1 − X ÷ 100)
Worked examples
A discount
A jacket costs $80 and is 15% off. 15% of 80 = 0.15 × 80 = $12, so the sale price is $80 − $12 = $68. Use “Decrease Y by X%” to get $68 directly.
A test score
You scored 30 out of 120. 30 ÷ 120 = 0.25, and 0.25 × 100 = 25%. Use “X is what % of Y”.
Growth
Monthly sales rose from 50 to 65. (65 − 50) ÷ 50 × 100 = +30%. Use “% change from X to Y”.
Percentages in everyday life
Percentages appear in shopping, banking, grades, nutrition labels, sports statistics and news headlines. The skill is not the arithmetic; it is choosing the right base, the number the percentage is measured against. A “25% off” coupon is measured against the original price. A “25% increase in traffic” is measured against last month's traffic. When two percentages come from different bases they cannot simply be added.
Quick reference: common percentages
| Percent | Fraction | Decimal | Mental shortcut |
|---|---|---|---|
| 10% | 1/10 | 0.1 | Move the decimal point one place left |
| 20% | 1/5 | 0.2 | Find 10% and double it |
| 25% | 1/4 | 0.25 | Halve, then halve again |
| 50% | 1/2 | 0.5 | Divide by 2 |
| 75% | 3/4 | 0.75 | Find 25% and multiply by 3 |
Tips and tricks
To calculate a tip of 18%, find 10% (move the decimal), then add 8% by taking 10% again and subtracting a fifth of it. To check a sale price, multiply by (1 − discount): a 30% discount means you pay 70%, so multiply the price by 0.7. For a price that includes tax, remember that the tax is a percentage of the pre-tax price, so dividing the total by (1 + tax rate) recovers the pre-tax amount.
Successive percentage changes
Two changes in a row multiply rather than add. A price up 10% and then up 10% again is × 1.1 × 1.1 = × 1.21, a 21% rise. A stock that falls 50% must then rise 100% to recover. This asymmetry is why percentage losses feel bigger than the equal percentage gain.
Practice problems
Try these yourself first, then check your answer. The answers come from the calculator above.
- What is 35% of 240?
Show answer
35% of 240: 84
- A phone drops from $800 to $680. What is the percent change?
Show answer
Change from 800 to 680: -15%
- A $60 meal gets an 18% tip added. What is the total?
Show answer
60 increased by 18%: 70.8
Common mistakes to avoid
- Percent change is measured against the starting value. A rise from 50 to 65 is +30%, but a fall from 65 back to 50 is only −23.08%.
- A 20% increase followed by a 20% decrease does not return you to the start: 100 → 120 → 96.
- Percentage points and percent are different. Going from 10% to 12% is +2 percentage points but a 20% relative increase.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For example, 15% of 80 is 0.15 × 80 = 12.
How do I find percent change?
Subtract the old value from the new value, divide by the old value, then multiply by 100. A positive result is an increase and a negative result is a decrease.
Can a percentage be more than 100?
Yes. 150% of 40 is 60. Percentages above 100 describe amounts larger than the whole, such as a price that has more than doubled.
How do I reverse a percentage increase?
Divide the new value by (1 + rate). If a price is $230 after a 15% rise, the original was 230 ÷ 1.15 = $200.
Reviewed September 26, 2026 by the SolveCalcPro editorial team. Found a mistake? Tell us; see our editorial policy.