Percentage Change: Your Questions Answered
These are the questions people ask most often about percentage change. Each answer is short; follow the links for the full detail.
What does a percentage change calculation tell me?
Calculates the percentage increase or decrease.
What is the formula?
% change = (new − old) ÷ |old| × 100.
What do I need to enter?
Old value, New value.
Can I use any units?
Yes, as long as every input uses the same unit. The answer will be in that unit (squared for areas, cubed for volumes).
Can you show an example?
For example, with these inputs:
- Old value: 80
- New value: 100
the calculator returns:
- Change: 25.00%
- Difference: 20
Any tips?
- For exam work, show your method; marks are often given for working, not just the answer.
- When numbers are very large or small, scientific notation makes them easier to compare.
- Round only at the final step to avoid accumulated rounding errors.
Background
Each formula has assumptions built in. Area formulas assume flat shapes, volume formulas assume regular solids and statistical measures assume the data you enter is the data you want to describe. Knowing the assumptions helps you pick the right tool.
Calculators are best used to check working rather than replace it, especially for exams where method marks count. Work the problem by hand first, then confirm with the calculator.
Rounding is a common source of small errors. Keep full precision during intermediate steps and round only the final answer to the number of decimal places or significant figures the question asks for.
Related calculations
- Percentage Difference Calculator: Compares two values relative to their average.
- Average (Mean) Calculator: Finds the arithmetic mean of a list.
- Median Calculator: Finds the middle value of a list.
- Mode Calculator: Finds the most frequent value(s).
Try it yourself with the Percentage Change Calculator.
Run your own numbers: Percentage Change Calculator