Percentage Calculator
Calculate percentages, percentage change and percentage of a total.
About Percentage Calculator
Percentage Calculator handles three related questions: finding a percentage of a value, expressing one value as a percentage of another, and measuring percentage change between a starting and ending value. Select the calculation type first so the two input labels match the question you are asking.
Use it for a discount amount, a share of a total, or a change in a measured quantity. The same numbers can mean different things in each mode: 15% of 2,000 gives an amount, while 15 out of 2,000 gives a percentage. Results update as you type. The calculator returns the percentage calculation itself; it does not automatically subtract a discount from the original price or add taxes.
How to use Percentage Calculator
- Choose the question
Select X% of Y, X is what % of Y, or % change from X to Y in Calculation type.
- Read the labels
Check whether X is a percentage, a part, or a starting value before entering the numbers.
- Enter both numbers
Enter X and Y. Percentage-of-total needs a nonzero total; percentage change needs a nonzero starting value.
- Use the result
Read the automatically updated Result. Use Copy or Print, or change modes for another question.
Example: A discount amount
Choose X% of Y, enter 15 and 2,000, and the result is 300. For a discount, subtract that amount from 2,000 yourself: the final price would be 1,700.
How it works
In X% of Y mode, the tool divides X by 100 and multiplies by Y. In X is what % of Y mode, it divides the part X by the total Y and multiplies by 100. In change mode, it subtracts the starting value X from the ending value Y, divides by X and multiplies by 100. The result receives a percent sign in the latter two modes, but not when calculating an amount.
The denominator defines the comparison. Going from 100 to 120 is a 20% increase, while going from 120 back to 100 is about a 16.67% decrease because the starting value changed. Percentage points are different again: moving from a 10% rate to 15% is a five-percentage-point difference, not a 5% relative increase. Results are rounded for display to four decimal places.
When is this useful?
- Find a discount or tax amount.
- Express a completed quantity as a share of a total.
- Compare a starting and ending measurement.
Things to know
- The result is not automatically added to or subtracted from a price.
- A zero denominator is rejected for share and change modes.
- Percentage change with negative starting values can be unintuitive; interpret the chosen baseline carefully.
Privacy & processing
All three modes run as local arithmetic in this browser. The input values are not submitted to a ToolMyth calculation API.
Frequently asked questions
Why do the input labels change?
Each mode asks a different question. The labels identify whether the numbers are a rate and amount, part and total, or starting and ending values.
Why can I not calculate a change from zero?
The formula divides by the starting value. Division by zero cannot produce a meaningful finite percentage change.
Are a percentage and percentage points the same?
No. A rise from 10% to 15% is 5 percentage points, or a 50% relative increase compared with the starting rate.
Why is my reverse percentage change different?
Reversing X and Y changes the denominator. An increase and its reversing decrease usually have different percentages.