Quick answer
Use Percentage Calculator when you need a fast answer for percent-of math, percent increase or decrease, a discount, a markup, or a reverse percentage. Reverse percent now separates a known part from a final value after an increase or decrease, so choose the setup that matches the wording of your problem.
If the question is just a sale price, the Percent Off Calculatoris faster. If you are adding tax after a price, use the Sales Tax Calculator.
Start with the mode
- Choose the percentage question that matches your problem.
- Type the numbers into the fields for that mode.
- Press Calculate percentage.
- Read the answer, formula line, and steps.
- Copy the answer if you need it in notes, homework, a message, or a spreadsheet.
Which mode should I pick?
Percent of a number: answers questions like 18% of 240.
What percent? answers questions like 25 is what percent of 200.
Percentage change: compares an original value with a new value.
Add or subtract percent: handles discounts, markups, tax, tips, and growth.
Reverse percent: finds a whole from a known part, or the original value before an increase or decrease.
Five examples that cover most searches
Three reverse percentage formulas
Choose Part is % of whole when you know a part and its percentage. The original whole is the known part divided by the percentage as a decimal. For 30 at 15%, calculate 30 / 0.15 = 200.
Choose After increase when the final value already includes a rise. A 20% increase makes the final value 120% of the original, so 120 / 1.20 = 100. Choose After decrease when the final value is smaller. A 20% decrease leaves 80%, so 80 / 0.80 = 100.
Do not subtract 20% of 120 to reverse a 20% increase. That calculates 20% from the larger final value and returns 96. The original increase used 100 as its base, so division by 1.20 is the correct reversal.
Examples from the percentage calculator
43.2
12.5%
27.5% decrease
150
200
Original value = 100
Original value = 100
Discounts, tips, tax, and markups
For a discount, choose Add or subtract percent, enter the original price, enter the discount percent, and choose Decrease. A $120 item with 25% off becomes $90 because 25% of 120 is 30, and 120 - 30 = 90.
For tax, tips, markup, or growth, use the same mode and choose Increase. The result shows the final value, and the formula line shows the amount added or subtracted.
Percent change mistake to avoid
Percent change needs a starting point. If a price drops from 160 to 116, the original value is 160. Avoid swapping the numbers. If you reverse them, you are asking how much 116 would need to rise to get back to 160.
The whole value cannot be zero in a what-percent question. The original value cannot be zero in a percentage-change question. A part-of-whole reverse percentage cannot use 0%. A reverse decrease must stay below 100% because a 100% decrease leaves no recoverable positive original value from the final amount.
What the formula line means
The calculator shows the short math behind the answer. For percent-of questions, it uses value x percent / 100. For what-percent questions, it uses part / whole x 100. For percent change, it divides the change by the original value. Then it turns that result into a percent.
This matches the school idea of percent as "per 100." OpenStax explains percent this way. Khan Academy uses the same part, whole, increase, and decrease setup in percent practice.
Double-check before using the result
Double-check the mode, the starting value, and the sign on the result. A decrease should look like a decrease. A markup should make the number bigger. A discount should make it smaller.
Avoid using this page as the final rule for a store, class, tax form, or business policy. The calculator shows the math. The real rule still comes from the receipt, teacher, spreadsheet, or official policy.
History, privacy, and copying
Recent percentage answers stay visible in the current page while you work. This is useful when comparing discounts, prices, growth rates, or percentage changes. The tool keeps only a short list in the current browser tab. It is not sent to a server.
Copy answer copies the displayed answer to your clipboard so you can paste it into notes, homework, a spreadsheet, or a message.
Sources and limits
This guide checked the page against OpenStax percent basics, OpenStax percent applications, Khan Academy percentage-change practice, and BBC Bitesize reverse percentages.
The calculator is for checking math. That is the limit. It does not decide the real store price, tax rule, coupon rule, school grading rule, or business markup policy for you.