Percentage Change Calculator
Work out how much something rose or fell as a percentage.
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The percentage change calculator tells you how much something has risen or fallen between two moments, as a percentage. Enter the starting and final values and the result appears instantly, positive for a rise and negative for a fall.
How it is calculated
The difference is always measured against the starting value:
| From | To | Operation | Change |
|---|---|---|---|
| 80 | 100 | (100 − 80) / 80 | +25% |
| 100 | 80 | (80 − 100) / 100 | −20% |
| 50 | 150 | (150 − 50) / 50 | +200% |
| 1,200 | 1,020 | (1,020 − 1,200) / 1,200 | −15% |
The asymmetry trap
This is the most common misreading of percentages: a rise and a fall of the same size do not cancel out.
If a £100 price rises by 20%, it becomes £120. If it then falls by 20%, it does not return to £100 but to £96, because that second 20% is taken from 120 and not from 100. Undoing a 20% rise takes a 16.67% fall.
It is why something that rises 50% and then falls 50% ends up 25% cheaper than it started (from 100 to 150 and then to 75), and why a portfolio that loses 50% needs to gain 100% to recover.
How to use Percentage change
- 1
Enter the starting value
In the first field put the "before" figure, for example the price something had last month.
- 2
Enter the final value
In the second field put the "after" figure. Order matters, because the change is always measured against the starting value.
- 3
Read the change
A positive result is a rise and a negative one a fall. It appears instantly, with no button to press.
- 4
Copy the result
Use the copy button to take the percentage with you.
Frequently asked questions
How do you work out percentage change?
Subtract the starting value from the final one, divide by the starting value and multiply by 100. From 80 to 100 the change is (100 − 80) / 80 × 100 = +25%.
Why don't a rise and a fall give the same percentage?
Because it is always measured against the starting value, which differs by direction. Going from 80 to 100 is 20 over 80, a 25% rise; going from 100 to 80 is the same 20 but over 100, a 20% fall.
What does a negative result mean?
That the final value is lower than the starting one, in other words a drop. A −15% means 15% of the starting figure has been lost.
Can it go above 100%?
Yes, as soon as something more than doubles. From 50 to 150 the change is +200%. Downwards, though, the floor is −100%: nothing can fall further than to zero.
What if the starting value is zero?
There is no percentage change, because that means dividing by zero. Any growth from zero is mathematically infinite, so the calculator leaves the result empty.