Percentage Calculator
Pick the percentage question you actually have, fill in the sentence, and see every step of the working.
Details
What do you want to work out?
25% of 80 = 20
Result
20
What is 25% of 80?
This calculator handles the everyday percentage questions in one place: a percentage of a number, one number as a percentage of another, an increase or a decrease, and working backwards from a result to the original figure.
Pick the question you actually have from the list, fill in the sentence, and it returns the answer along with every step of the working, so you can follow how it got there.
What is a percentage?
A percentage is just a way of saying how much of something you have, out of 100. The word means per hundred. So 25% means 25 out of every 100, which is the same as a quarter.
Percentages exist so you can compare things fairly. Scoring 18 out of 20 and 43 out of 50 are hard to compare as they are. As percentages they become 90% and 86%, and it is instantly obvious which is better.
Any percentage can be written three ways, and they all mean the same thing: 25%, the fraction 25/100, and the decimal 0.25. To turn a percentage into a decimal, divide by 100. To go back, multiply by 100.
The number after the word 'of' is almost always the whole, so it is the one you divide by. Multiplying by 100 at the end is what turns the decimal 0.25 into 25%.
What to enter
- The basics
- For the two everyday questions: what is 20% of 250, and 15 is what percentage of 60.
- Up & down
- For increases and decreases. Use it for a pay rise, a price cut, or a bill that went up.
- Work backwards
- When you know the result but not the starting number. A jacket costs $80 after 20% off, so what was the original price?
- Several at once
- Applies more than one percentage in a row, like a 20% discount followed by 10% off at the till.
- Other
- Less common jobs, including percentage difference between two numbers.
How to calculate a percentage
There are really only three questions, and each is one line of arithmetic.
- part
- The amount you have
- whole
- The total it came out of
A percentage of a number. Divide the percentage by 100, then multiply. 20% of 250 is 0.20 x 250 = 50.
One number as a percentage of another. Divide the part by the whole, then multiply by 100. 15 out of 60 is 15 / 60 = 0.25, so 25%.
An increase or decrease. Find the difference, divide by the ORIGINAL number, then multiply by 100. Dividing by the wrong number here is the most common mistake people make.
See a worked example: a price rising from $40 to $50
- Original price
- $40
- New price
- $50
Find the difference: 50 - 40 = 10.
Divide by the ORIGINAL price, not the new one: 10 / 40 = 0.25.
Multiply by 100: 0.25 x 100 = 25.
Careful going the other way. If that $50 price drops back to $40, that is not a 25% fall. The difference is still 10, but now you divide by 50, which gives 20%.
A 25% increase
Frequently asked questions
- How do I calculate a percentage of a number?
Divide the percentage by 100, then multiply by the number. For 30% of 80: 30 / 100 = 0.3, and 0.3 x 80 = 24.
A quick shortcut for 10%: just move the decimal point one place left. 10% of 80 is 8. From there, 30% is simply three lots of that, so 24.
- How do I work out what percentage one number is of another?
Divide the smaller number by the bigger one, then multiply by 100. If you scored 18 out of 20: 18 / 20 = 0.9, and 0.9 x 100 = 90%.
The number after the word 'of' is almost always the one you divide by.
- What is the percentage formula?
There is only one, and every percentage question is a rearrangement of it: part ÷ whole × 100 = percentage.
Looking for the part instead? Multiply: whole × percentage ÷ 100. Looking for the whole? Divide: part ÷ percentage × 100. Whichever of the three you are missing, the other two get you there.
- When should I use percent difference instead?
When you are comparing two numbers and neither one is the original — two quotes for the same job, two measurements of the same thing.
Dividing by either value would be an arbitrary choice, so you divide by the average of the two instead. That is the percent difference calculator.
- Why isn't a 50% rise cancelled out by a 50% fall?
Because the second percentage is taken from a different starting number. Take $100, add 50%, and you have $150. Take 50% off that and you are at $75, not back to $100.
The rise was 50% of $100, but the fall was 50% of $150. Percentages always refer back to whatever number they were applied to, which is why order matters.
- What's the difference between percentage change and percentage points?
They are different things and mixing them up is genuinely misleading. If an interest rate goes from 2% to 4%, that is a rise of 2 percentage points, but it is a 100% increase.
Use percentage points when comparing two figures that are already percentages. Use percentage change for everything else.
- How do I add or remove a percentage in one step?
To add 15%, multiply by 1.15. To take 15% off, multiply by 0.85. This saves working out the amount and then adding it separately.
To go backwards, divide instead. If a price is $92 after 8% was removed, the original was 92 / 0.92 = $100.
Problems people actually run into
Discounts stacked on discounts are smaller than they look
A 20% sale with an extra 10% at the checkout is not 30% off. The second discount comes off the already reduced price, so $100 becomes $80, then $72. That is 28%, not 30%.
Retailers are not doing anything wrong here, but the wording invites you to add the two numbers together. The discount calculator handles stacked reductions directly. Use the Several at once mode to see what you actually pay.
Results are estimates for general information only and are not professional financial, medical, or legal advice. Read our full disclaimer.
Last updated: August 29, 2026
