Percentage Change Calculator
Measure the increase or decrease between two values.
Percentage change
Original value must be nonzero. Uses the absolute original value as the baseline.
Formula checked · NumberSwift · Review process
How this calculator works
The absolute difference and relative percentage answer different questions. A rise from 80 to 100 adds 20 units and increases the original amount by 25%. Reversing the comparison gives a 20% decrease. A zero starting value has no defined percentage change, even though the absolute difference is meaningful.
Formula
change % = (new − old) / |old| × 100
Assumptions & limitations
Original value must be nonzero. Uses the absolute original value as the baseline.
Sources & reference material
- OpenStax: understanding percent ↗
Reference for percentages and decimal proportions.
Worked example
80 to 100 is a 25% increase.
To apply a known increase or discount instead of finding the rate, use the Percentage Calculator in Increase or Decrease mode.
Our approach to calculations ↗Common questions
Why must the original value be nonzero?
Relative change divides by the original magnitude. Division by zero has no finite percentage interpretation.
Why are the reverse percentages different?
The baseline changes. Going from 80 to 100 is +25%; going from 100 to 80 is −20%.
What does Difference mean?
It is the new amount minus the original amount in the input units, separate from the relative percentage.