About Reverse Percentage Calculator
This calculator finds the original number when you know an amount and what percent of the whole it is. If 45 is 15% of a number, enter 45 and 15 and it returns 300. It is free, needs no sign-up and runs in your browser, so nothing you enter is uploaded.
The common use is finding a price before a discount or before tax. If a jacket costs 68 after a 15% discount, you paid 85% of the original, so the original is 68 ÷ 0.85 = 80. A frequent mistake is to add 15% back onto 68, which gives 78.2 and is wrong, because 15% was taken from the larger original number.
The percent cannot be zero, because no amount is zero percent of a positive whole.
How to use Reverse Percentage Calculator
- Choose the mode that matches your question, for example "X% of Y" or "% change".
- Fill in the fields. Each field is labelled in the sentence, such as "Percent" and "Number".
- Each mode opens with a worked example already filled in; change the numbers and the answer updates as you type, with no calculate button.
- Open the working underneath to see the formula and each step of the arithmetic.
- For a discount or a tip, leave the optional tax or people field empty to ignore it.
- If a field would make the sum impossible, such as a zero whole, the calculator tells you which one instead of showing a wrong number.
Features
- Sixteen modes in one place, from percent of a number to a tip split.
- Formula and step-by-step arithmetic shown for every answer.
- Percentage change measured against the absolute starting value, so a negative start still gives a sensible direction.
- Percentage difference that treats both values equally, kept separate from percentage change.
- Reverse percentage for finding the original price or total.
- Discount mode with optional sales tax applied after the discount, plus the amount you save.
- A margin and markup mode that shows profit, margin on price and markup on cost side by side.
- Percent error for lab work and marks percentage for exam results, with marks lost.
- Fraction to percent, percent to fraction and percent to decimal conversions, with fractions reduced to lowest terms.
- Tip calculator with an optional number of people to split the total.
Reverse percentage formula
Divide the amount by the percent as a decimal.
whole = amount ÷ (percent ÷ 100)Worked examples
45 is 15% of what? gives 300
45 ÷ 0.15 = 300.
Price after a 15% discount is 68 gives Original 80
You paid 85% of the original. Enter 68 and 85: 68 ÷ 0.85 = 80.
Privacy: how it works
- Everything is calculated by code running in your browser tab. The numbers you enter are not sent to Ulkaa or to any other server, and there is nothing to sign in to.
Tips
- Percentage change cannot start from zero, since there is no base to measure against. The calculator says so rather than showing infinity.
- To add or take off a percentage in one step, multiply by 1 plus or minus the decimal. Adding 15% is × 1.15 and taking off 15% is × 0.85.
- Percent points and percent are not the same thing. A rate moving from 10% to 12% is up 2 percentage points but up 20% in relative terms.
- Results keep ten significant figures, so a very small value such as 0.0000042 is not rounded to zero. For money, round the final figure to your currency.
Frequently asked questions
Is it really free?
Yes. There is no price, no trial and no credit card. Ulkaa Tool does the work with your own device, so there is no server bill to pass on to you.
Do I need an account?
No. There is no sign-up and no login. Open the page and use it. An Ulkaa account is not needed for anything on this tool.
Does it run in my browser?
Yes. Your numbers are processed by code running in your browser tab, on your own device.
Is my data uploaded?
No. Your numbers are never sent to Ulkaa or to anyone else. You can check this yourself by watching the Network tab in your browser developer tools while you use the tool.
How do I find the original price after a discount?
Work out the percent you paid, which is 100 minus the discount, then divide the sale price by it as a decimal. For 68 after 15% off, divide by 0.85 to get 80.
How do I remove tax from a price that includes it?
Divide by 1 plus the tax rate. A total of 230 with 15% tax included has a net price of 230 ÷ 1.15 = 200.
More Percentage Calculator pages
- Percentage CalculatorPick the question you are asking, enter two numbers and see the answer with its formula.
- What Is X Percent of Y?Enter a percent and a number to get that share of it.
- X Is What Percent of Y?Enter a part and a whole to see the part as a percentage.
- Percentage Increase CalculatorFind how much a value went up, as a percentage of where it started.
- Percentage Decrease CalculatorFind how much a value fell, as a percentage of where it started.
- Percentage Change CalculatorFind the change between two values as a share of the starting value.
- Percentage Difference CalculatorCompare two values that are equals, with no before or after.
- Add a Percentage to a NumberIncrease any number by a percent and get the new total.
- Subtract a Percentage From a NumberReduce any number by a percent and get what is left.
- Discount CalculatorEnter a price and a percent off to see what you pay and what you save.
- Percent Error CalculatorCompare a measured value with the true value as a percentage.
- Marks Percentage CalculatorEnter the marks you scored and the total to get your percentage.
- Fraction to Percent CalculatorEnter a numerator and a denominator to get the percent.