Percent Calculator
Percentage Calculator works out Answer and Part from Percentage (%), Whole / base / original value and Part / amount. The default figures on this page give answer of 30; change any entry and the result, the working and the sources update together.
Your figures
Updates as you typeHow this is worked out
2 steps
- Write the percent as a decimal: 15% / 100 = 0.15
- Multiply by the whole: 0.15 x 200 = 30
Its 7 worked examples are re-run on every release, last on 15 September 2026. What changed
What the Percentage Calculator calculates
Works out a percentage of a number, what percent one number is of another, the original whole behind a part, the result of increasing or decreasing a value by a percentage, and a full percentage table listing each percentage of a number alongside its decimal and fraction.
How to use this Percentage Calculator
Enter Percentage (%), Whole / base / original value, Part / amount and Table: first percentage. Answer updates as you type, and “Use a worked example” loads checked figures you can adjust. Change one figure at a time to see what drives the result.
How the result is worked out
Open “How this is worked out” beside the result for the step-by-step calculation behind Answer, Part and Whole.
The method follows National Institute of Standards and Technology, SI Guide (NIST SP 811) §7.10.2 on percent as the number 0.01 and OpenStax, Prealgebra 2e, Chapter 6 "Percents" (solving percent applications with the basic percent equation).
15% of 200 example
With What do you want to work out?: percent-of, Percentage (%): 15, Whole / base / original value: 200, the calculator returns Answer: 30, Part: 30. This example is checked against an independent source in the test suite.
What you can compare
Change one input at a time to see how it affects Answer, Part and Whole. The inputs you can vary are Percentage (%), Whole / base / original value, Part / amount, Table: first percentage, Table: last percentage and Table: step between rows.
Results are general information, not financial, tax, legal, medical or engineering advice. Check any decision that matters with a qualified professional.
See something wrong? Report a problem with this calculator
Frequently asked questions
What information do I need for the Percentage Calculator?
You need Percentage (%), Whole / base / original value, Part / amount, Table: first percentage, Table: last percentage and Table: step between rows. The page opens with default figures that give answer of 30, so you can see the scale before entering your own.
What does this Percentage Calculator show?
It shows Answer, Part, Whole, Percentage, Percent as a decimal, Percent as a fraction, Amount of change and Value after the change, with the working and any warnings for your entries.
Can I check how the Percentage Calculator result was calculated?
Yes. The “How this is worked out” section shows the calculation steps, and the sources section identifies the references used for the method.