About PercentChangeFormula.com

PercentChangeFormula.com is a small set of free calculators for the percentage questions people actually get stuck on: percent change, increase and decrease, percent difference, percent error, compound growth, reverse percentages and percentage points.

How we build the calculators

• Every answer shows its working, so you can check it and learn the method rather than just copy a number.
• Edge cases are handled honestly. Percent change from zero is reported as undefined rather than as 0% or infinity, and negative starting values use the absolute-value convention.
• The worked examples are tested. Every example on the site is checked by automated tests against the same code the calculators use.
• Nothing leaves your device. All calculations run in your browser. See the privacy page.

Who runs it

The site is built and maintained by StepOne Digital Agency. If you spot an error or want a calculator added, please get in touch.