Choose one of the three modes using the tabs at the top: find X% of a number, find what percent one number is of another, or calculate the percentage change between two values. Enter your numbers and the result updates instantly. Use the copy or print buttons to save your result.
To find X% of Y, multiply Y by X and divide by 100. Equivalently, convert the percentage to a decimal (divide by 100) and multiply: Result = Y × (X ÷ 100). For example, 15% of 80 = 80 × 0.15 = 12. A useful mental math trick: 10% of any number is found by moving the decimal one place left. Double it for 20%, halve it for 5%, add them for 15%, and so on.
To find what percent X is of Y, use: Percentage = (X ÷ Y) × 100. For example, what percent is 30 of 120? (30 ÷ 120) × 100 = 25%. This is useful for test scores (you got 45 out of 60 — what percent?), discount amounts, or comparing any two numbers as a ratio.
Percentage change = ((New − Old) ÷ Old) × 100. A positive result is an increase; negative is a decrease. Examples: a salary rising from $60,000 to $66,000 is a 10% increase. A stock falling from $200 to $150 is a 25% decrease. Note: a 50% drop followed by a 50% gain does not return you to the starting point — you end up 25% below where you started, because the percentage is calculated on a different base each time.
If you know the result and the percentage but need the original number, divide the result by the percentage as a decimal: Original = Result ÷ (Percentage ÷ 100). For example, if $45 is 75% of some price, the original = 45 ÷ 0.75 = $60. This is handy for finding the original price of a discounted item, figuring out a pre-tax amount from a total with tax, or reversing any percentage calculation.
This distinction matters more than most people realize. A percentage point is an absolute difference between two percentages. A percentage change is a relative change. If an interest rate rises from 2% to 3%, that's a rise of 1 percentage point — but it's a 50% increase in the rate. News articles and politicians frequently conflate these, so it's worth being aware of the difference when reading about interest rates, poll results, or tax changes.
Tip: 20% tip on $75 = 75 × 0.20 = $15. | Discount: 30% off $120 = 120 × 0.70 = $84. | Tax: $200 plus 8% tax = 200 × 1.08 = $216. | Score: 38 out of 45 = (38 ÷ 45) × 100 = 84.4%. | Markup: $50 cost with 40% markup = 50 × 1.40 = $70 selling price.
Other free tools on CalcNova you might find useful: