Which number is the percentage based on?
The starting value is the reference point for a percentage change. When something rises from 80 to 100, the gain of 20 is one-quarter of the original 80, even though 20 is only one-fifth of the new 100.
What we put into the calculator
Both numbers measure the same thing in the same units. The initial value is positive: 80 units. The new value is 100 units. There are no rates, discounts, or compounding involved.
The numbers behind the result
| Starting value | 80.00 |
|---|---|
| Ending value | 100.00 |
| Difference (100 − 80) | 20.00 |
| Difference ÷ starting value | 0.25 |
| Percentage change | +25.00% |
What the result means
Percentage change is (new − original) ÷ original × 100. Reversing the journey does not undo the percentage: moving from 100 down to 80 is a 20% decrease, because now the starting point is 100. This is why “up 25%, then down 25%” does not return to the original value.
Try changing one assumption
Switch the starting and ending values to see −20%. Then try a starting value of 50 and new value of 75. Keep the same unit for both entries to make the comparison meaningful.
Open calculator with these inputs ↗Where the estimate stops
A zero starting value makes ordinary percentage change undefined; this calculator requires a positive original value. Percent change also does not explain the cause or importance of the change.
Calculation method: The displayed sample result is checked against the same JavaScript formula that powers the calculator. No live quotes, rates or financial data are implied.