Calculators
Percentage Change Calculator
Measure the percentage increase or decrease between two numbers, or work backwards: what was the original value before a known change?
Percentage change between two values
Reverse: original value before the change
Formula: (new − old)/|old| × 100. Reverse mode: old = new/(1 + change/100). Runs locally.
Why +25% Followed by −25% Is Not Zero
Percentage changes compound, they do not cancel: +25% on 100 is 125, and −25% on 125 is 93.75 — a net −6.25%. The change is always relative to where you started, so equal-looking ups and downs leave you worse off. (The same asymmetry is why a 50% drop needs a 100% gain to recover.)
The Formula Behind the Result
- Enter the old (starting) and new (ending) values.
- The tool reports the signed percentage change and labels it as increase or decrease.
- Reverse mode: enter a new value and a percentage to recover the original value before the change.
- The formula is displayed with your actual numbers substituted in.
Worked Example
Common Questions
Why does going up 10% and then down 10% not return to the start?
Each percentage applies to a different base. 100 → 110, then 110 − 11 = 99. Percentage changes compound, they do not cancel.
How is a change from 50 to -10 handled?
The tool reports the change against the absolute baseline and flags results that cross zero, where percentage change becomes less meaningful.
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