Reviewed 6 November 2026. This practical guide explains the decisions and checks that help you use the related tool correctly.
Understand the task
To find x percent of a number, multiply the number by x and divide by 100. For example, 15% of 800 is 120. To find what percent 72 is of 90, calculate 72 ÷ 90 × 100 = 80%. The whole must not be zero.
Important details to check
For percentage change, subtract the original value from the new value, divide by the original value and multiply by 100. A positive result is an increase and a negative result is a decrease. Reversing the comparison can produce a different percentage because the reference value changes.
Recommended workflow
Choose the type of percentage problem, enter the relevant values, check that the base is correct and round only at the end.
Step-by-step checklist
- Read the instructions for the file, assignment or service you are working with.
- Keep an unchanged copy of important source material.
- Use the related tool and review the result instead of assuming every conversion is perfect.
- Check the output in the application or context where it will actually be used.
Frequently asked questions
Is a 50% increase followed by a 50% decrease back to the start? No. The second rate applies to the increased amount. Can percentage change be negative? Yes.