Percentage change
(new − old) ÷ old × 100. Positive is an increase.
How to use the Percentage change
What does the Percentage change do?
Percent increase or decrease from an old value to a new value; It applies this page-specific rule: percent change always starts from the old value.
Which inputs does this calculator use?
To percent increase or decrease from an old value to a new value, enter Old, New; keep every value in the same example; the page then updates the result from the current values; Start with a familiar case covered by this rule - A 10% rise followed by a 10% fall does not return to the start (100 → 110 → 99) - so the expected result can confirm the settings.
How should the calculator result be read?
For a result intended to percent increase or decrease from an old value to a new value, a 10% rise followed by a 10% fall does not return to the start (100 → 110 → 99); read new together with the original old rather than as an isolated answer, and confirm that its units or structure match the intended use.
10% up then 10% down?
When the goal is to percent increase or decrease from an old value to a new value, not back to start.
What if old is zero?
When using the page to percent increase or decrease from an old value to a new value, the percent is undefined.
Limits and accuracy
When using this calculator to percent increase or decrease from an old value to a new value, this page is not a compound-interest or tax tool; check the entered values, units, rounding, and assumptions before using the answer for an important decision; keep old until the output has been checked in its intended destination. For a repeatable check when you need to percent increase or decrease from an old value to a new value, record Old alongside the final output and selected options.
How this works
Percent change always starts from the old value. If a price goes from 50 to 65, the change is 15 and 15/50 = 30%. Going back from 65 to 50 is not −30%; it is −15/65 ≈ −23.08%.
A 10% rise followed by a 10% fall does not return to the start (100 → 110 → 99). Run this calculator twice if you need each leg.
This page is not a compound-interest or tax tool. It is one ratio.
Frequently asked questions
10% up then 10% down?
Not back to start. 100 → 110 → 99. Use this tool twice.
What if old is zero?
The percent is undefined. The page says so.
Is decrease shown negative?
Yes. The sign is the direction.