Percentage Calculator
Choose the percentage question you want to answer and see the formula alongside the result.
Browser-based · No signup · Transparent assumptions
- 01Enter your values
- 02Adjust your settings
- 03Review your results
| Calculation | Result |
|---|
Rounding changes the display only. Symmetric difference requires nonnegative inputs.
Calculations run in this browser. Shared URLs can contain input values. Review links before sharing financial, dietary or birth-date information.
When to use this calculator
Check a price discount, recover an original amount from a percentage change or compare two values. Choose change for a directional before-and-after question and difference for the supported symmetric comparison.
Review the worked example and assumptions below, then use the supported report or copy controls to keep the result with its inputs. Calculations run in this browser; a shared URL can include the values you entered.
How to use Percentage Calculator
- Select percent of, percent is, change, reverse, add/subtract or symmetric difference.
- Enter both values; use a signed percentage for reverse changes.
- Review the base and formula before copying or exporting the result.
Percentage change versus percentage difference
Percentage change divides the signed difference by the starting value. Symmetric difference divides the absolute difference by the average of two nonnegative values. Reverse percentage divides a final value by the applied multiplier; it does not simply subtract the percentage.
Worked example
20% of 250 = 50
Change from 100 to 120 = +20%
Reverse a 20% increase: 120 / 1.2 = 100Assumptions and limits
A zero base makes percent-is and percent-change undefined. A reverse change of -100% cannot recover a unique original value. Symmetric difference is restricted to nonnegative quantities with a nonzero mean. Decimal arithmetic uses floating-point numbers.
Reference: MDN: JavaScript numbers. Model/source review: 19 October 2026. See the tool-specific scope and precision limits above.
Frequently asked questions
Is a fall from 120 to 100 also 20%?
No. It is about -16.67% because the starting base is 120.
How do I reverse a discount?
Choose reverse percentage and enter the discount as a negative change, such as -20%.
Why is a zero starting value rejected?
Percentage change divides by the starting value, and division by zero is undefined.
A practical input scenario
Choose the operation that matches your question, enter the values and inspect which input acts as the base for the displayed percentage.
Read the scope alongside the result
Percentage change and symmetric difference use different bases. Undefined zero-base cases and arithmetic limitations remain described on the page.