Percentage change calculator
Find how much one number is bigger or smaller than another in percent. Use this calculator to compare two values or measure a percentage increase or decrease, with the original value as your reference.
Result for the values shown.
Calculations run in your browser.
What to enter
| Input | Meaning and units |
|---|---|
| Original value | The reference value used as the denominator. Reversing the comparison changes the percentage. |
| New value | The value you want to compare with the original reference. |
Understanding your result
A positive result means the new number is numerically greater; a negative result means it is smaller. The original value sets the reference, so reversing the two numbers changes the answer.
Common mistakes
- Reversing the reference and comparison values.
- Confusing percentage change with what percent one value is of another, or with percentage points.
Check your calculation
- Check 80 → 100 = +25% and 100 → 80 = −20%. A zero reference has no defined percentage change.
Calculation checks, sources and review limits
How much bigger or smaller is one number than another in percent?
Choose which number is the reference, then compare the other number with it. Enter the reference in Original value and the number you are comparing in New value. With a positive reference, a positive result means the new number is bigger; a negative result means it is smaller.
Common uses
- Compare a new price with an old price.
- Measure a salary increase or decrease.
- Compare sales or quantities across two periods.
How it works
This calculator answers: “How much bigger or smaller is this number compared with the reference number, in percentage terms?” Enter the reference number in Original value and the number you want to compare in New value. Subtract the original from the new value, divide by the absolute original value, then multiply by 100. For a positive original value, this is the usual percentage-change formula. A positive result means the new number is larger; a negative result means it is smaller. For example, a change from 80 to 100 is a 25% increase. Reversing the comparison, from 100 to 80, is a 20% decrease because the reference has changed. With negative starting values, this tool explicitly uses the magnitude of the original value as its denominator. A zero reference has no defined percentage change.
Worked example
100 is 25% bigger than 80: (100 − 80) ÷ 80 × 100 = 25%. In the other direction, 80 is 20% smaller than 100: (80 − 100) ÷ 100 × 100 = −20%. Always choose the reference number first.
FAQ
How do I find how much bigger one number is than another in percent?
Enter the reference number as Original value and the number you want to compare as New value. With a positive reference, calculate (new − original) ÷ original × 100. For 80 as the reference and 100 as the new value, the result is 25%.
How do I find how much smaller one number is than another in percent?
Keep the reference number in Original value. If the new number is smaller, the result is negative: 100 to 80 gives −20%, meaning the new value is 20% smaller than the reference.
Does the order of the two numbers matter?
Yes. The reference determines the denominator. 100 is 25% bigger than 80, while 80 is 20% smaller than 100.
Is this the same as finding what percent one number is of another?
No. “100 is what percent of 80?” gives 125%. “How much bigger is 100 than 80?” gives a 25% increase. This calculator answers the increase-or-decrease question.
Is percentage change the same as a symmetric percentage difference?
Percentage change compares with a chosen starting value. A common symmetric percentage-difference formula compares two non-negative values relative to their average. That answers a different question and does not use this calculator’s baseline formula.