Percentage Calculator
Percent of, percent change, increase and decrease. Runs in your browser.
About this percentage calculator
This percentage calculator answers the five percentage questions people ask most, all on one screen. Find a percent of a number, work out what percent one number is of another, measure the percentage change between two values, add or subtract a percentage, and find the whole when you only know a part.
Each answer updates as you type and comes with the formula filled in with your own numbers. You can check the working, copy the answer, or reuse the formula in a spreadsheet.
It handles the details that trip up quick calculations: negative numbers, division by zero and floating point noise such as 0.30000000000000004. Everything runs in your browser.
Features
Five calculators on one page
Percent of a number, X as a percent of Y, percentage change, increase or decrease by a percent, and finding the whole from a part.
Formula shown with your numbers
Every result lists the exact formula used, such as 15 ÷ 100 × 200 = 30, so you can follow and repeat the math.
Change and difference side by side
The percentage change card also shows the symmetric percentage difference, so you can tell the two apart.
Clean numbers
Results are rounded to 10 significant digits with thousands separators, which hides floating point noise without losing useful precision.
Plain explanations instead of errors
If an answer would need division by zero, the card tells you why there is no answer instead of showing NaN or Infinity.
One-click copy
Copy any result as a plain number without separators, ready to paste into a spreadsheet or form.
How to use the percentage calculator
- 1Pick the calculation you need.
- 2Enter the numbers.
- 3The answer updates instantly.
When to use it
Shopping discounts
Decrease a price by 25% to see the sale price and how much you save.
Tips and tax
Find 18% of a bill for a tip, or increase a price by a sales tax or VAT rate.
Grades and scores
Work out what percent 42 correct answers out of 50 is.
Business growth
Measure the percentage change in sales, traffic or prices from one period to the next.
Working backwards
If 45 people are 30% of a group, find the full group size.
The percentage formulas, in plain English
A percent is a number out of 100, so 15% means 15 hundredths, or 0.15. Every percentage question comes down to one relationship: part = percent ÷ 100 × whole. Rearrange it and you get the other formulas.
- Percent of a number: P ÷ 100 × Y. 15% of 200 = 30.
- What percent X is of Y: X ÷ Y × 100. 30 of 120 = 25%.
- Percentage change: (new − old) ÷ |old| × 100. 50 to 65 = 30% increase.
- Increase or decrease: Y × (1 ± P ÷ 100). 80 decreased by 25% = 60.
- Whole from a part: X ÷ (P ÷ 100). 45 is 30% of 150.
Percentage change vs percentage difference
Percentage change has a direction. It compares a new value to a starting value, so going from 50 to 65 is a 30% increase, while going from 65 to 50 is about a 23% decrease. The starting value is the base.
Percentage difference has no direction. It compares the gap between two values to their average, so 50 and 65 are about 26% apart whichever comes first. Use change for before and after figures, and difference when neither value is the reference.
When the starting value is negative, this calculator divides by its absolute value. That way a move from −50 to −25 reads as a 50% increase, which matches the direction the number actually moved.
Percent vs percentage points
If an interest rate goes from 4% to 5%, it rose by 1 percentage point. In percent terms it rose by 25%, because 1 is a quarter of 4. News reports mix these up often.
Use percentage points for the plain gap between two percentages. Use percent change when you want the size of the move relative to where it started. You can get the second from the percentage change card by entering 4 and 5.
Why a 50% drop needs a 100% rise to recover
Percentages after a change apply to a different base. If a price of 100 falls 50%, it becomes 50. A 50% rise on 50 only brings it to 75. To get back to 100 you need a 100% rise.
The same effect means a 20% discount followed by 20% tax doesn't return you to the original price. Try it in the increase or decrease card.
Why use Mavros
| Mavros | Typical upload sites | |
|---|---|---|
| Calculations | Five common types on one screen | Separate pages for each question |
| Formula | Shown with your numbers for every answer | Hidden or explained only in general terms |
| Results | Live as you type | Calculate button, sometimes a reload |
| Division by zero | A plain explanation | NaN, Infinity or an empty box |
| Ads | None in the way of the answer | Ads between inputs and results |
| Privacy | Runs in your browser | Inputs may be sent to a server |
Tips
- To find a sale price, use Decrease with the discount rate. The formula line also shows how much you save.
- To add tax or VAT, use Increase with the tax rate.
- Enter decimals freely, such as 7.5%. Inputs accept any precision.
- Percent values above 100 are valid. Doubling a number is a 100% increase.
- Copy gives a plain number with no thousands separators, so it pastes cleanly into spreadsheets.
Questions
How do I calculate a percentage of a number?
Divide the percent by 100 and multiply by the number. For 15% of 200, that is 0.15 × 200 = 30. The first card does this for you.
How do I find what percent one number is of another?
Divide the part by the whole and multiply by 100. 30 out of 120 is 30 ÷ 120 × 100 = 25%.
How is percentage change calculated?
Subtract the old value from the new one, divide by the absolute value of the old one, and multiply by 100. A positive result is an increase and a negative one is a decrease.
What is the difference between percentage change and percentage difference?
Percentage change measures a move from a starting value, so direction matters. Percentage difference compares the gap to the average of both values and has no direction. The calculator shows both.
How do I add a percentage to a number?
Multiply the number by 1 plus the percent divided by 100. Adding 20% to 50 gives 50 × 1.2 = 60. Use the Increase option.
How do I calculate a discount?
Use the Decrease option with the discount rate. 80 decreased by 25% is 60, and the formula line shows the 20 you save.
How do I find the original number from a percentage?
Divide the part by the percent over 100. If 45 is 30% of a number, the number is 45 ÷ 0.30 = 150. The last card does this.
Why can't I calculate a percentage change from 0?
Any change from zero would be an infinitely large percentage, because the formula divides by the starting value. The calculator explains this instead of showing an error.
Is my data sent anywhere?
No. All calculations run in your browser.