How to calculate percentage change
- Enter the old (starting) value and the new value in the first card.
- The percentage change appears with a + sign for an increase and − for a decrease, along with the absolute difference.
Formula
Percentage change = (new − old) ÷ |old| × 100. From 80 to 100 the change is (100 − 80) ÷ 80 × 100 = +25%. From 100 back to 80 it is (80 − 100) ÷ 100 × 100 = −20%. The two are different because each is measured against its own starting value, which is why a 50% loss needs a 100% gain to recover.
Use percentage change for prices, sales, salaries, website traffic, exam scores and investment returns over time. When neither value is the "before", such as comparing two shops' prices, use percentage difference instead, shown in the second card: it divides the gap by the average of the two values, so the order does not matter.
If the old value is 0, percentage change is undefined: any increase from zero is infinitely large in relative terms, so report the absolute change instead. For changes in rates that are already percentages, such as interest rising from 4% to 5%, say "1 percentage point" (or 25%) to avoid confusion.
FAQ
How do I calculate percentage increase?
Subtract the old value from the new one, divide by the old value and multiply by 100. From 50 to 65: 15 ÷ 50 × 100 = 30%.
Can percentage change be more than 100%?
Yes. Going from 20 to 60 is a 200% increase. A decrease can never be more than 100%.
Why is a 20% drop not undone by a 20% rise?
The rise is calculated on the smaller number. 100 → 80 is −20%, but 80 → 100 is +25%.