Percentage Calculator
Pick a mode, enter Percent (X) and Number (Y), then click Calculate. You can find X percent of Y, increase Y by X percent, or decrease Y by X percent, and see the equation with the numeric answer in the result box.
Updated 2026-08-03 · math
About this tool
The Mode menu offers three formulas. X% of Y multiplies Y by X/100. Increase adds that percentage to Y. Decrease subtracts it. Both inputs must be finite numbers; otherwise the tool shows Enter valid numbers. Results are computed in the browser when you press Calculate—there is no live auto-calc while typing.
How to use
- Open the calculator: Load this page so Mode, Percent (X), Number (Y), and Calculate appear.
- Choose a mode: Select X% of Y, Increase Y by X%, or Decrease Y by X% from the menu.
- Enter X and Y: Type the percent in Percent (X) and the base value in Number (Y).
- Calculate: Click Calculate and read the equation plus answer in the result area.
Common use cases
- Work out a discount amount as a percent of a price.
- Apply a tax or tip-style increase to a base number.
- Reduce a value by a percentage for markdowns or shrinkage estimates.
Tips
- Choose the correct Mode before clicking Calculate; the labels explain each formula.
- X is the percent and Y is the base number—do not swap them by habit.
- Invalid or empty numbers produce Enter valid numbers instead of NaN.
FAQ
What does X% of Y return?
It returns Y multiplied by X/100, shown like 25% of 200 = 50.
How does Increase Y by X% work?
It computes Y × (1 + X/100), for example 200 + 25% = 250.
How does Decrease Y by X% work?
It computes Y × (1 − X/100), for example 200 − 25% = 150.
Why do I see Enter valid numbers?
One or both inputs are not finite numbers; fix X and Y, then calculate again.