Percentage Calculator
A percentage is a number out of a hundred, so x% of y is x ÷ 100 × y. Type 15 and 200 into the X% of Y tab and this calculator returns 30. Four more tabs handle the questions that follow: add 15% to 200 gives 230, subtract it gives 170, 30 out of 200 is 15%, and a move from 80 to 100 is a 25% change.
About Percentage Calculator
Five tabs cover the five percentage questions people actually ask, and each is a different formula rather than the same one relabelled. X% of Y multiplies: 15 and 200 give 30. Increase by % adds the share back on, so 200 raised by 15% is 230. Decrease by % takes it off, giving 170. What percent divides one number by another and multiplies by 100, so 30 out of 200 is 15%. Percent change compares a From value with a To value, and 80 to 100 is a 25% increase.
Two of those deserve attention. Increase and decrease are not symmetric: 200 raised by 15% is 230, but 230 reduced by 15% is 195.5, not 200, because the percentage is taken from a bigger base the second time. And percent change divides by the starting value, which is why going from 80 to 100 is a 25% rise while going back from 100 to 80 is a 20% fall — the same 20 units against a different base.
Results are rounded to two decimal places, and the fields stay empty until you fill them, with placeholders showing a worked example for each tab. Any blank or non-numeric field leaves the result as a question mark rather than showing a wrong number, and two divisions are guarded: What percent needs a non-zero total, and Percent change needs a non-zero starting value, because neither has an answer otherwise.
The arithmetic runs in your browser and nothing is sent anywhere. What it does not do is compound anything: it applies one percentage once, so successive discounts, interest over several periods or a percentage of a percentage have to be run one step at a time.
Use Cases
How to use
Pick the tab that matches your question: X% of Y, Increase by %, Decrease by %, What percent, or Percent change.
For X% of Y, type the percentage in the small box and the value in the wide one; the answer appears as you type.
For Increase by % or Decrease by %, put the starting value first and the percentage second; the sign between the boxes shows which way it goes.
For What percent, enter the part in the first box and the total in the second, and read the result as a percentage.
For Percent change, fill From value with the earlier number and To value with the later one; a negative result means a decrease.
Read the large result, which is rounded to two decimal places, and switch tabs to ask a different question about the same numbers.
Pro Tips
- Increase and decrease do not cancel out. Add 15% to 200 and you get 230; take 15% off 230 and you get 195.5, because the second percentage is taken from the larger number.
- In Percent change, From is the starting value and the divisor. Swapping the two fields does not just flip the sign: 80 to 100 is +25%, while 100 to 80 is −20%.
- Results are rounded to two decimals, so a repeating figure such as 47 out of 60 shows as 78.33%. Multiply the raw numbers yourself if you need more precision than that.
- A question mark instead of a number means a field is empty or not numeric, or that the divisor is zero. The tool refuses to guess rather than printing a misleading result.
- For a percentage of a percentage, run the tool twice: 20% of 50% of 800 is 20% of 400, which is 80. There is no compounding mode, so chain the steps deliberately.
Troubleshooting
The result shows a question mark instead of a number.
One of the fields is empty or not a number, or the division has no answer: What percent needs a total other than zero, and Percent change needs a starting value other than zero. Fill in both boxes with numbers and the result appears immediately.
Adding and then removing the same percentage does not return the original number.
That is arithmetic, not a bug. A percentage is always taken from whatever number it is applied to, so 200 plus 15% is 230, and 15% of 230 is 34.5, leaving 195.5. To undo an increase of p percent, divide by 1 plus p over 100 instead of subtracting.
Percent change gives a different number depending on the order of the two values.
It should, because the From value is the base of the calculation. Going from 80 to 100 adds 20 to a base of 80, which is 25%; going from 100 to 80 removes 20 from a base of 100, which is 20%. Put the earlier figure in From value.
Frequently Asked Questions
A percentage is a share of a hundred, so x% of y is x ÷ 100 × y. On the X% of Y tab, 15 and 200 return 30. The other four tabs rearrange the same idea: adding or removing a percentage, finding what percent one number is of another, and measuring the change between two numbers.
Multiply the starting value by the percentage and add it back on: 200 increased by 15% is 200 + 30, which is 230. The Increase by % tab does exactly that. If instead you want the percentage between two known numbers, use Percent change, which divides the difference by the earlier value.
Use Decrease by %. Enter the original price first and the discount second: 60 with 30% off leaves 42. To check a claimed discount instead, put the original in From value and the sale price in To value on the Percent change tab; the negative result is the real discount.
Divide the part by the total and multiply by 100. The What percent tab does it: 30 out of 200 is 15%, and 47 out of 60 is 78.33% after rounding to two decimals. The second box must be a total other than zero, otherwise the answer is undefined and the tool shows a question mark.
Subtract the earlier value from the later one, divide by the earlier value and multiply by 100. From 80 to 100 that is 20 ÷ 80, a 25% increase. The Percent change tab expects From value to be the earlier figure, and a negative result means a decrease.
Because a percentage is always relative to its starting point. Both moves are 20 units, but 20 out of 80 is 25% while 20 out of 100 is 20%. This is why a stock that falls 50% then rises 50% is still down: the recovery is measured against the smaller number.
Use What percent with your score as the first number and the maximum as the second: 47 out of 60 is 78.33%. For several papers, add all the marks scored and all the marks available first, then run the division once, rather than averaging percentages of different totals.
Use Increase by % with the net amount first and the rate second, because the charge is a percentage of the net figure. To go the other way, from a total that already includes the rate back to the net amount, divide by 1 plus the rate — subtracting the percentage from the total overshoots.
Run the calculator twice, since it applies one percentage at a time. 20% of 50% of 800 means 50% of 800 first, which is 400, then 20% of 400, which is 80. The same approach applies to two successive discounts, which never add up to their sum.
Every answer is rounded to two decimal places, so 47 out of 60 appears as 78.33% rather than 78.3333. That is enough for prices, marks and reporting; for anything that has to reconcile to the cent over many rows, keep the unrounded numbers in a spreadsheet and round only at the end.