Percent Change Calculator
How much did it change, in percent? Enter the before and after values — get the increase or decrease instantly.
About this tool
Percent change is the most misused number in everyday maths, because the denominator matters: it is always the original value. A price rising from $80 to $100 has risen 25% (25 ÷ 80). If it falls back to $80, that is a 20% decrease (20 ÷ 100) — which is why a 25% gain is not undone by a 25% loss.
This calculator shows the signed percentage change and spells out the difference in plain words, so you can sanity-check headlines, salary changes, weight goals, portfolio moves and grade improvements. It costs nothing and runs in your browser.
How to use it
- Enter the original (starting) value in “From”.
- Enter the new value in “To”.
- Read the percentage change: positive means an increase, negative a decrease.
Frequently asked questions
How is percent change calculated?
Percent change = (new − old) ÷ |old| × 100. Dividing by the original value is what makes it a relative change: going from 80 to 100 is +25%, and going back from 100 to 80 is −20% — the two directions are not mirror images.
Can percent change be more than 100%?
Increases can be any size — doubling is +100%, tripling is +200%. Decreases cannot pass −100% while the value stays at or above zero, because a value cannot fall below zero; if the new value is itself negative, the decrease runs past −100% and the calculator says so.
What if the starting value is negative?
The formula uses the absolute value of the starting number, the common convention in finance and reporting. One caution: a change that crosses zero (from a negative start to a positive value, or the reverse) is not meaningful as an ordinary percent change, and the calculator flags it when it happens.