# Percentage Calculator

> Calculate percentages, increases, and changes instantly. Free percentage calculator with the formula shown - runs entirely in your browser, no signup.

- **Canonical URL:** https://boringtoolskit.com/percentage-calc/
- **Category:** Finance & Investing
- **Evidence level:** authored-methodology
- **Reviewed:** July 26, 2026
- **Last verified:** 2026-10-12
- **Privacy:** Inputs and results stay in this browser unless the page clearly labels an external request.

## How it works

The calculator supports: X% of Y = X ÷ 100 × Y; X is what % of Y = X ÷ Y × 100; percent change = (new − original) ÷ |original| × 100.

## Worked example

15% of 80 is 12. Moving from 80 to 100 is a 25% increase. Moving from 100 to 80 is a 20% decrease.

## Assumptions

- Percent change depends on the chosen base value.
- Original value cannot be zero for percent-change calculations.
- For taxes, fees, APR, discounts, or legal calculations, confirm the exact rule being applied.

## Common questions

### Why are percentage increase and decrease not symmetric?

Because each uses its own starting value as the denominator.

### What does percentage point mean?

A move from 5% to 7% is 2 percentage points, not a 2% relative increase.

### Can I use this for discounts or tax?

Yes for arithmetic, but tax/fee rules can add exceptions, caps, or rounding.

## Related tools

- /profit-margin-markup-calculator/
- /sales-tax-vat-calculator/
- /general-scientific-calculator/

## Sources

- [Calculation methodology](/methodology/)
- [Quality evidence and verification standard](/quality-evidence/)

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