Percentage Calculator
Find what X% of a number is, what percent one number is of another, percent increase or decrease, or the whole from a known part.
Last updated July 29, 2026
How to use the percentage calculator
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Pick a tab: X% of Y, X is what % of Y, % change, or Find the whole.
- 2
Enter the two numbers requested for that mode.
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Your answer updates instantly as you type, no button to click, and it works with decimals and negative numbers too.
The four percentage formulas, with examples
1. X% of Y (find the part)
Formula: (percent ÷ 100) × number
Example 1: What is 20% of 150? (20 ÷ 100) × 150 = 0.2 × 150 = 30.
Example 2: A restaurant bill is $64.00 and you want to leave a 18% tip. (18 ÷ 100) × 64 = 0.18 × 64 = $11.52 tip, for a total of $75.52.
Example 3: A $250 jacket is 30% off. The discount amount is (30 ÷ 100) × 250 = $75, so the sale price is $250 − $75 = $175.
2. X is what percent of Y (find the percent)
Formula: (part ÷ whole) × 100
Example 1: 30 is what percent of 150? (30 ÷ 150) × 100 = 0.2 × 100 = 20%.
Example 2: You scored 42 out of 50 on a test. (42 ÷ 50) × 100 = 0.84 × 100 = 84%.
Example 3: Out of 220 total orders, 11 were returned. (11 ÷ 220) × 100 = 5% return rate.
3. Percent change (increase or decrease)
Formula: ((new − original) ÷ original) × 100
Example 1 (increase): Rent goes from $1,200 to $1,350. ((1,350 − 1,200) ÷ 1,200) × 100 = (150 ÷ 1,200) × 100 = +12.5%.
Example 2 (decrease): A stock drops from $80 to $68. ((68 − 80) ÷ 80) × 100 = (−12 ÷ 80) × 100 = −15%, a 15% decrease.
Example 3 (why order matters): A price rises 20%, then falls 20%. Starting at $100: up 20% gives $120, then down 20% of $120 (not of $100) gives $120 − $24 = $96, not back to $100. Each percent change is calculated against the value at that step, not the original.
4. Find the whole (reverse percentage)
Formula: part ÷ (percent ÷ 100)
Example 1: 30 is 20% of what number? 30 ÷ (20 ÷ 100) = 30 ÷ 0.2 = 150.
Example 2: A $12 tip was 15% of the bill. The bill total is 12 ÷ 0.15 = $80.
Example 3 (reversing an increase): After a 20% price increase, an item costs $72. Because $72 represents 120% of the original price (100% + 20%), the original price is 72 ÷ 1.20 = $60. That's not the same as 72 minus 20% of 72, which would incorrectly give $57.60.
Percentage quick reference
| Percent | Fraction | Decimal | Of $100 |
|---|---|---|---|
| 10% | 1/10 | 0.10 | $10 |
| 12.5% | 1/8 | 0.125 | $12.50 |
| 20% | 1/5 | 0.20 | $20 |
| 25% | 1/4 | 0.25 | $25 |
| 33.3% | 1/3 | 0.333 | $33.33 |
| 50% | 1/2 | 0.50 | $50 |
| 75% | 3/4 | 0.75 | $75 |
A fast mental-math trick: 10% of any number just moves the decimal point one place left (10% of 150 = 15). From there, 5% is half of that (7.50), and 20% is double it (30). Handy for estimating tips and discounts without pulling out a calculator.
Everyday uses for percentage math
Percentages show up constantly because they let you compare values of very different sizes on the same scale. A $5 discount means something different on a $10 item (50% off) than on a $500 item (1% off), and the percentage is what tells you that, not the raw dollar amount.
Sale tags, coupon codes, and cashback offers are almost always a percentage of the original price. Use the "X% of Y" mode to find the discount amount, then subtract it from the price. Got stacked discounts (a coupon on top of a sale), or need to work backward from a sale price? Our Discount / Sale Price Calculator handles the full chain automatically.
Restaurant tips run 15-20% of the pre-tax bill by convention, and splitting a bill with tax and tip across a group is a lot easier once you actually know the percentage amount instead of eyeballing it.
Working out how much a price grows after tax, or reversing a tax-included total back to the pre-tax price, is the same percentage math pointed in different directions. Our Sales Tax Calculator handles both directions directly, with quick state-rate lookups.
A score reported as "42/50" is hard to compare against a differently-scaled test until you convert it to a percentage (84%) using the "X is what percent of Y" mode. Once you know what letter grade that maps to, our GPA Calculator turns a full course list into a semester or cumulative GPA.
Interest rates, loan APRs, investment returns, and inflation are all percentages, and percent change over time (this quarter vs. last, this year vs. last) is how financial performance gets reported almost everywhere.
Survey results, poll numbers, and error rates get reported as percentages of a total sample precisely so results from different sample sizes stay comparable.
Curious how your weight relates to a healthy range instead of raw pounds or kilograms? Our BMI Calculator applies the same idea of comparing a value against a standard scale.
Need to convert a measurement instead of a percentage, like kilograms to pounds or Celsius to Fahrenheit? Our Unit Converter covers length, weight, volume, temperature, and more.
Splitting a restaurant bill and figuring out the tip? Try the Tip Calculator →