How to Calculate Percentage Change: A Step-by-Step Guide
Calculates the percentage increase or decrease.
These calculations come up in school, at work and in daily life, from PSLE and O-Level practice to measuring a room for new flooring. Doing them by hand builds understanding, and a calculator lets you check the answer instantly.
What you need
- Old value
- New value
Step by step
- Enter the old value.
- Enter the new value.
- The results update as you type, or press Calculate.
- Read the change first, then the supporting figures below it.
The formula
% change = (new − old) ÷ |old| × 100.
Worked example
For example, with these inputs:
- Old value: 80
- New value: 100
the calculator returns:
- Change: 25.00%
- Difference: 20
A second example
Now change the inputs to:
- Old value: 100
- New value: 100
the calculator returns:
- Change: 0.00%
- Difference: 0
Practical tips
- For exam work, show your method; marks are often given for working, not just the answer.
- Round only at the final step to avoid accumulated rounding errors.
- Write down the formula before plugging numbers in; it prevents mixing up variables.
- Use brackets to make the order of operations explicit.
Background
A quick mental estimate before calculating is a powerful check. If a room's floor area comes out at 4,000 square metres or a percentage comes out above 100% when it should not, you know to look again.
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.
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).
Want to skip the arithmetic? The free Percentage Change Calculator does all of this instantly and updates as you type.
Run your own numbers: Percentage Change Calculator