Percentage Calculator - Calculate Percent of a Number
Solve any percentage problem in seconds — find a percent of a number, work out what percent one number is of another, or reverse-engineer the original value from a percentage.
Pick the type of percentage problem, enter your two numbers, and get an instant answer with the formula used.
Percentage Calculator - Calculate Percent of a Number
Solve any percentage problem in seconds — find a percent of a number, work out what percent one number is of another, or reverse-engineer the original value from a percentage.
Use this mode to find a percentage of a total — perfect for discounts, tips, tax, commission, or markup.
About the percentage calculator
A percentage is simply a fraction expressed out of one hundred. When you say "15 percent", you mean fifteen parts out of every hundred — written 15% or 0.15. Because the denominator is fixed, percentages let you compare proportions across totals of any size, which is why they sit at the heart of pricing, taxes, statistics, grades, finance, science and everyday shopping decisions.
The percentage calculator handles the three problems that account for the vast majority of real-world percent questions. The first is "What is X% of Y?" — multiply Y by X then divide by 100. Use it to compute a sales tax, a tip, a commission, a discount amount, a markup, or any share of a known total. The second is "X is what percent of Y?" — divide X by Y then multiply by 100. Use it when you already have a part and a whole and need to express the part as a percentage, such as turning a test score of 45 out of 50 into a clean 90%. The third is "X is Y% of what?" — divide X by Y then multiply by 100. Use it to reverse a discount and find the original price, or to back-solve a base figure when only a percentage of it is known.
The formulas are deliberately symmetrical. If you call the percentage P, the part A and the whole B, the underlying identity is always A = (P / 100) × B. The three calculator modes simply rearrange that identity to solve for whichever variable is missing. Internally the percentage calculator performs the division and multiplication in standard IEEE-754 double-precision arithmetic, so results are accurate to ten significant digits for any practical input.
A few common pitfalls to keep in mind. A 20% discount followed by a 20% increase does not return you to the original price — percentages of different bases do not cancel. Likewise, going from 4% to 5% can be described as a one percentage-point increase or a 25% relative increase; both are correct but they answer different questions. When you are stacking percentages — sales tax on a discounted item, compound interest over multiple periods, or a tip computed on a post-tax bill — apply each percent to the running total in the order it actually occurs, and never simply add the percentages together.
Whether you are budgeting, grading, pricing a product, calculating tip on a restaurant bill, comparing year-over-year growth, working out a body-fat ratio, or studying for a math exam, the three modes in the percentage calculator cover almost every percentage question you will ever need to answer. Bookmark the page and let it do the arithmetic so you can focus on what the numbers mean.
Percentage calculator examples
Three quick scenarios that show each calculation mode in action with real numbers.
| Input | Result | Explanation |
|---|---|---|
| What is 25% of $150? | $37.50 | Use mode "What is X% of Y?". Multiply 150 by 25 then divide by 100. This is the dollar value of a 25% discount on a $150 item. |
| 45 is what percent of 50? | 90% | Use mode "X is what percent of Y?". Divide 45 by 50 to get 0.9, then multiply by 100. A score of 45 out of 50 on an exam is 90%. |
| 60 is 80% of what? | 75 | Use mode "X is Y% of what?". Divide 60 by 80 to get 0.75, then multiply by 100. If a sale item costs $60 and that is 80% of the original, the original price was $75. |
| What is 18% of $78.50? | $14.13 | Use mode "What is X% of Y?". Multiply 78.50 by 18 then divide by 100. This is a standard 18% restaurant tip on a $78.50 bill. |
How to use the percentage calculator
- Choose the calculation type that matches your question: "What is X% of Y?", "X is what percent of Y?", or "X is Y% of what?".
- Enter the two known numbers in the input fields. The field labels update to match the mode you selected.
- Click Calculate. The answer appears below, together with the formula in plain English so you can double-check the math.
- Click Reset to clear both fields, or pick a different mode and re-enter values to solve a related problem.
- Tap any of the example buttons under the worked examples to instantly load real numbers into the percentage calculator.
Percentage calculator FAQ
How do I calculate a percentage of a number by hand?
Convert the percent to a decimal by dividing by 100, then multiply by the number. For 25% of 150, compute 0.25 × 150 = 37.5. The calculator does exactly this internally for any percent and any number.
What is the difference between a percent and a percentage point?
A percentage point is the arithmetic difference between two percentages. Moving from 4% to 5% is a one percentage-point change but a 25% relative increase (1 ÷ 4 = 0.25). Confusing the two is a common source of misleading statistics in news headlines.
How do I find the original price before a discount?
Use the "X is Y% of what?" mode. If the sale price is $60 and represents 80% of the original price (i.e. a 20% discount), enter 60 and 80; the calculator returns 75. The general formula is original = sale ÷ (1 − discount%/100).
How do I add tax or tip to a bill?
Use the "What is X% of Y?" mode to find the tax or tip amount, then add it to the original bill. For an 18% tip on $78.50, the calculator returns $14.13, so the total is $92.63. To get the post-tip total in one step, multiply the bill by 1.18.
Can a percentage be more than 100?
Yes. Percentages above 100% simply mean more than the whole. A stock that grew from $50 to $150 has grown by 200% of its starting value (an increase of $100 is 200% of $50). The calculator handles values above 100% without any special configuration.
Are the calculations accurate enough for finance and accounting?
The results are accurate to ten significant digits, which is more than enough for retail pricing, taxes, tipping, grades, and everyday finance. For regulated accounting work where rounding rules matter, always apply your jurisdiction's specific rounding convention to the displayed result.