About Percentage Calculator
This percentage calculator is free, needs no sign-up and runs in your browser, so the numbers you type are never uploaded. It covers the questions people actually ask: what is 15% of 200, 30 is what percent of 120, how much did a price change, what is the price after a discount, and what number is 45 if 45 is 15% of it.
Every result comes with the formula and the arithmetic written out, so you can check it or copy the method into homework. Choose a mode, fill in the fields and the answer updates as you type. The modes are listed under the calculator and each one also has its own page with worked examples.
There are sixteen modes in all: percent of a number, part of a whole, percentage change, increase, decrease, percentage difference, reverse percentage, discount with optional tax, margin and markup, percent error, marks percentage, fraction to percent, percent to fraction, percent to decimal and a tip splitter.
How to use 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.
The formulas behind each mode
Almost every percentage question is the same relationship with a different unknown: part = percent ÷ 100 × whole. Solve it for the part, for the percent or for the whole and you have the three basic modes. Increase, decrease, change and discount are built on top of it.
The calculator writes the formula for your mode above the arithmetic, so the table below is a reference rather than something you need to memorise.
part = percent ÷ 100 × whole
percent = part ÷ whole × 100
whole = part ÷ (percent ÷ 100)
change % = (new − old) ÷ |old| × 100
new value = old × (1 ± percent ÷ 100)Worked examples
What is 8.5% of 240? gives 20.4
8.5 ÷ 100 × 240 = 20.4.
Price 120, 30% off, 8% tax gives Final price 90.72
Discount 120 × 30 ÷ 100 = 36, so the price is 84. Tax on 84 is 84 × 8 ÷ 100 = 6.72. Final: 84 + 6.72 = 90.72.
68 is 85% of what number? gives 80
Divide by the percent as a decimal: 68 ÷ 0.85 = 80.
Percentage change from 80 to 100 gives +25%
(100 − 80) ÷ 80 × 100 = 25. Going back from 100 to 80 is a fall of 20%, not 25%, because the base is different.
Which mode answers which question
| Mode | Question | Formula |
|---|---|---|
| X% of Y | What is 15% of 200? | percent ÷ 100 × number |
| X is what % of Y | 30 is what percent of 120? | part ÷ whole × 100 |
| % change | From 80 to 100? | (new − old) ÷ |old| × 100 |
| Increase by % | Add 15% to 200 | number × (1 + percent ÷ 100) |
| Decrease by % | Take 15% off 200 | number × (1 − percent ÷ 100) |
| % difference | How far apart are 50 and 70? | |a − b| ÷ ((a + b) ÷ 2) × 100 |
| Reverse % | 45 is 15% of what? | amount ÷ (percent ÷ 100) |
| Margin and markup | Cost 60, sold at 80 | profit ÷ price, profit ÷ cost |
| % error | Measured 9.6, true 10 | |measured − true| ÷ |true| × 100 |
Good to know
Percent change, percent difference and percent error are different questions
Percent change has a direction and an old value: it asks how much something moved from where it started. Going from 50 to 60 is +20%, and from 60 back to 50 is about −16.67%. Percent difference has no direction: it compares two values that are equally valid, using their average as the base, so 50 and 70 are 33.33% apart whichever order you give them. Percent error compares a measurement with a known true value and is always shown as a positive size of error.
Pick the one that matches the story. Prices over time are change, two quotes from two shops are difference, and a lab reading against a textbook value is error.
Why +50% then −50% does not bring you back
Starting at 100, a rise of 50% gives 150. A fall of 50% from 150 gives 75, not 100, because the second percentage is taken from a bigger base. To undo a rise of p percent you need a fall of p ÷ (100 + p) × 100 percent. For +50% that is 33.33%.
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 calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. For 15% of 200 that is 15 ÷ 100 × 200 = 30.
How do I calculate percentage increase?
Subtract the old value from the new value, divide by the old value and multiply by 100. From 50 to 60 that is (60 − 50) ÷ 50 × 100 = 20%.
What is the difference between percent change and percent difference?
Percent change uses the old value as the base and has a direction. Percent difference uses the average of the two values as the base and has no direction. Use change for before and after, difference for two peers.
How do I find the original price after a discount?
Use reverse percentage. If a price after a 15% discount is 68, the price paid is 85% of the original, so the original is 68 ÷ 0.85 = 80.
How do I calculate my marks percentage?
Divide the marks you got by the total marks and multiply by 100. Scoring 432 out of 500 gives 432 ÷ 500 × 100 = 86.4%.
Is tax added before or after the discount?
The discount mode takes the discount first and applies tax to the discounted price, which is how most shops charge. If your tax is charged on the full price, enter the discount as 0 and work the discount separately.
Why does the calculator refuse some inputs?
A few sums have no answer: a zero whole, a zero starting value for percent change, or a zero percent in reverse mode. The message names the field to fix.
Popular Percentage Calculator pages
- 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.
- Reverse Percentage CalculatorWork backwards from a part and its percent to the whole.
- 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.
- Percent to Fraction CalculatorWrite a percent as a simplified fraction.
- Percent to Decimal CalculatorTurn a percent into the decimal you can use in a formula.
- Tip CalculatorEnter the bill, the tip percent and the number of people.