About this tool
This calculator covers the four percentage calculations people search for most: finding a percentage of a number, finding what percent one number is of another, calculating percentage change between two numbers, and adding or subtracting a percentage from a number. All math runs in your browser.
How to use the Percentage Calculator
- Choose the calculation type that matches what you're trying to find.
- Enter your numbers in the fields that appear.
- Read the result — it updates as you type.
Common use cases
- Working out a tip, discount, or sales tax amount
- Finding a test score or grade as a percentage
- Calculating how much a price, salary, or metric changed year over year
- Adding a markup percentage or subtracting a discount from a price
Worked example
A $80 jacket marked 25% off: using "X% of Y" with 25 and 80 gives $20 off, so the sale price is $60. Checking your grade on a test where you got 42 out of 50: "X is what % of Y" with 42 and 50 gives 84%. Comparing rent that went from $1,200 to $1,350: "% increase/decrease" gives a 12.5% increase — calculated as the difference (150) divided by the original value (1,200), not the new one, which is a common point of confusion.
Things to watch out for
Percentage change is always calculated relative to the starting (original) value, not the ending value — a change from 200 to 100 is a 50% decrease, but going back from 100 to 200 is a 100% increase, not another 50%, because the base number is different each time. When stacking percentages (like a 20% raise followed by a 10% cut), each percentage applies to the current number at that point, not the original one, so the two changes don't simply add or cancel out.
For the difference between a percentage change and a percentage-point change — two things headlines often mix up — see Percentage Increase vs. Percentage Points.
The four formulas behind the calculator
- X% of Y:
Y × X ÷ 100. 15% of 60 = 9. - X is what % of Y:
X ÷ Y × 100. 9 of 60 = 15%. - % change from X to Y:
(Y − X) ÷ X × 100. 60 to 69 = 15% increase. - Add or subtract X% from Y:
Y × (1 + X ÷ 100), using a negative X to subtract. 60 + 15% = 69.
Results are rounded to two decimal places.
Reverse percentages: finding the original number
A common mistake is undoing a percentage by applying the same percentage the other way. If a price after 20% off is $64, adding 20% back gives $76.80, not the original. Divide instead:
- Before a discount:
original = sale price ÷ (1 − discount ÷ 100). $64 ÷ 0.80 = $80. - Before tax or a markup:
original = total ÷ (1 + rate ÷ 100). A $53.50 total with 7% sales tax came from $53.50 ÷ 1.07 = $50.
You can check the answer with the “Add or subtract a %” mode: 80 with −20 should give 64.
Percentage change vs percentage difference
Percentage change has a direction: it measures a new value against an old one. Percentage difference compares two values with no before and after, such as two store prices, and divides by their average: |A − B| ÷ ((A + B) ÷ 2) × 100. For 80 and 100 that gives 20 ÷ 90 × 100 = 22.22%. Percentage change gives 25% going from 80 to 100 and 20% going from 100 to 80. This calculator’s change mode answers the before-and-after question. Use the difference formula by hand when neither number is the starting point.
Tip chart
Tip amounts for common US tipping percentages, rounded to the cent. For other amounts, use “X% of Y” with the tip percentage and the bill.
| Bill | 15% | 18% | 20% | 25% |
|---|---|---|---|---|
| $20 | $3.00 | $3.60 | $4.00 | $5.00 |
| $40 | $6.00 | $7.20 | $8.00 | $10.00 |
| $50 | $7.50 | $9.00 | $10.00 | $12.50 |
| $75 | $11.25 | $13.50 | $15.00 | $18.75 |
| $100 | $15.00 | $18.00 | $20.00 | $25.00 |
| $150 | $22.50 | $27.00 | $30.00 | $37.50 |
A quick mental shortcut: 10% moves the decimal point one place left, so 20% is double that, and 15% is 10% plus half of 10%. On a $40 bill, 10% is $4, so 20% is $8 and 15% is $6.
Frequently asked questions
Divide the part by the whole and multiply by 100. For example, 25 out of 200 is (25 / 200) × 100 = 12.5%.
Percentage of a number gives you a portion of that number (like 20% of 50 = 10). Percentage increase/decrease compares two numbers and tells you how much one changed relative to the other, expressed as a percentage.
Because each percentage is calculated on a different base. A 50% increase on 100 gives 150; a 50% decrease on 150 gives 75, not 100 — the second percentage is taken from the new, larger number.
Divide the sale price by one minus the discount as a decimal. For a $45 item that was 25% off, the original price is 45 ÷ 0.75 = $60. Adding 25% back to $45 would give $56.25, which is wrong because the discount was taken from the larger original price, not the sale price.
Percentage change compares a new value with an old one and divides by the old value, so it has a direction and can be an increase or decrease. Percentage difference compares two values without a starting point and divides by their average. From 80 to 100 is a 25% increase, while their percentage difference is 22.22%.
Multiply the price by the tax rate divided by 100 to get the tax, then add it to the price. For a $49.99 item with 8.25% sales tax, the tax is 49.99 × 0.0825 = $4.12, so the total is $54.11. In this calculator, the Add or subtract a percent mode gives the total in one step.