Results are estimates, not financial or tax advice. Tax rates change; check the rate that applies to you with your tax office.
If a price of 115 includes a 15% increase, the original was 115 ÷ 1.15 = 100, not 115 − 15% = 97.75. After a 20% discount, a price of 80 started at 80 ÷ 0.8 = 100. Choose plus or minus and enter the final value and the percent.
How to use
- Pick a tab: Percentage, Discount, Margin or VAT / tax. Each also has its own page.
- In Percentage, choose the calculation (% of, What %, % change, Add / subtract, Reverse) and type two numbers. The answer updates as you type.
- In Discount, enter the price and tap a percentage. Add an extra % off or a coupon to stack discounts.
- In Margin, enter cost and selling price, or switch to Target margin or Markup to get the price you should charge.
- In VAT / tax, choose Add tax or Remove tax, enter the amount and tap a rate or type your own. Tap any result to copy it.
- Percentage change = (new − old) ÷ |old| × 100. Percentage difference compares two values to their average, so it’s the same in both directions.
- Reverse percentage divides by (1 + p/100): a price of 115 after a 15% increase was 100, not 97.75.
- Stacked discounts multiply: 20% off and then an extra 10% off is 28% off in total, not 30%.
- Margin is profit ÷ selling price; markup is profit ÷ cost. A 50% markup gives a 33.3% margin.
- Tax rates change and can differ by product and region (US sales tax adds city and county rates). The chips are common examples; check the rate that applies to you.
- Type decimals with a dot or a comma.
The formulas
X% of Y = Y × X ÷ 100, so 15% of 80 = 12. What percent A is of B = A ÷ B × 100, so 45 of 60 = 75%. Percentage change = (new − old) ÷ |old| × 100, so 80 → 100 is +25%.
Percentage difference compares two values to their average instead: |a − b| ÷ ((a + b) ÷ 2) × 100. For 80 and 100 that is 22.2%, the same in both directions. Use change when there is a before and after, difference when neither value is the reference.
Mistakes people often make
A rise and a fall of the same percent do not cancel: 100 + 20% = 120, but 120 − 20% = 96. To undo a 25% drop you need a 33.3% rise. And to find the price before a 15% increase, divide by 1.15 rather than subtracting 15%: 115 ÷ 1.15 = 100, not 97.75.
Percent vs percentage points
When a rate moves from 4% to 5%, it rose by one percentage point but by 25 percent. News reports on interest rates, polls and unemployment mix these up often, so it pays to check which one is meant.
Frequently asked questions
How do I calculate a percentage of a number?
Multiply the number by the percent and divide by 100. 20% of 150 is 150 × 20 ÷ 100 = 30.
How do I work out what percent one number is of another?
Divide the part by the whole and multiply by 100. 18 out of 24 is 18 ÷ 24 × 100 = 75%.
How do I calculate percentage increase?
Subtract the old value from the new one, divide by the old value and multiply by 100. From 50 to 65 is 15 ÷ 50 × 100 = 30%.
How do I reverse a percentage?
Divide the final value by 1 plus the percent as a decimal. A price of 230 that includes a 15% increase was 230 ÷ 1.15 = 200.
What is the difference between percentage change and percentage difference?
Change measures from a starting value (80 → 100 is +25%); difference compares two values to their average and is the same both ways (22.2% for 80 and 100).
Is a 50% increase followed by a 50% decrease back to the start?
No. 100 + 50% = 150, and 150 − 50% = 75. Each percent applies to a different base.