Percentage Calculator
Free percentage calculator.
The percentage calculator solves the three questions people ask most: what is X% of Y, X is what percent of Y, and X increased or decreased by Y%. Type your numbers and the answer updates instantly — no formulas to remember and nothing to submit.
Percentages turn raw numbers into something you can compare. A price drop, a test score, a tip, a commission, and a growth rate are all percentages underneath. Getting them right matters, and doing them in your head is where mistakes creep in.
How to use the percentage calculator
- Pick the tab that matches your question: a percentage of a number, what percent one number is of another, or a percentage change between two values.
- Enter your two numbers. Decimals are fine.
- Read the answer below — it recalculates as you type.
The formulas behind it
Every percentage question reduces to a fraction multiplied by 100.
- Percent of a number: result = (percent ÷ 100) × number. So 15% of 200 = 0.15 × 200 = 30.
- X is what percent of Y: percent = (X ÷ Y) × 100. So 45 out of 180 = 25%.
- Percentage change: change = ((new − old) ÷ old) × 100. Going from 80 to 100 is a 25% increase; going back from 100 to 80 is a 20% decrease.
That last asymmetry surprises people: a rise and the matching fall are not the same percentage, because the base you divide by changes.
Where you'll use it
Percentages show up everywhere money and measurement meet. Common cases include working out a discount at the checkout, splitting a tip, checking a sales tax line, reading a test score, sizing a commission, or comparing year-over-year growth. Whenever you need to compare two things fairly, converting to a percentage puts them on the same scale.
Worked examples
A few everyday scenarios make the three modes concrete. If a $60 shirt is marked 20% off, use "% of a number": 20% of 60 is 12, so you save $12 and pay $48. If you scored 38 out of 50 on a test, use "X is what %": 38 ÷ 50 × 100 = 76%. And if your rent rose from $1,200 to $1,320, use "increase / decrease": that's a 10% increase. Reversing it — from $1,320 back to $1,200 — is a 9.09% decrease, because the base you divide by is now larger. Keeping the base straight is the single most common source of percentage errors.
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100, then multiply by the number. For example, 20% of 150 is 0.20 × 150 = 30. The calculator does this for you under the '% of a number' tab.
Why isn't a 25% increase cancelled by a 25% decrease?
Because the base changes. A 25% rise from 80 gives 100. A 25% fall from 100 gives 75, not 80. To reverse a 25% increase you need a 20% decrease, since you're now dividing by the larger number.
Can I use decimals?
Yes. Every field accepts decimal values, so 12.5% of 47.9 works exactly as you'd expect.
Is my data sent anywhere?
No. The calculation runs entirely in your browser. Nothing you type leaves your device.
How do I add a percentage to a number?
Multiply the number by (1 + percent ÷ 100). To add 15% to 200, compute 200 × 1.15 = 230. To remove 15%, multiply by 0.85 instead.
How do I find the original price before a discount?
Divide the sale price by (1 − discount ÷ 100). If an item costs $48 after 20% off, the original was 48 ÷ 0.80 = $60.
Last updated: 2026-01-15