Percentage Decrease Calculator
Find the percentage decrease between two values, or reduce a starting figure by a percentage. The working is shown so you can check the result.
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Percentage decrease
20%
- Absolute change
- 20
- From
- 100
- To
- 80
((100 − 80) ÷ 100) × 100 = 20%
The formula
Percentage decrease measures a fall relative to the starting value. Subtract the new value from the old one, divide by the old value, and multiply by 100.
It is the same calculation as a percentage increase with the sign reversed, which is why one tool can answer both — but the wording matters when reporting the result.
Decrease % = ((Old − New) ÷ Old) × 100
- From 100 to 80 → ((100 − 80) ÷ 100) × 100 = 20% decrease
- From 250 to 100 → 60% decrease
- A fall to zero is always a 100% decrease.
Why percentage changes do not cancel out
A 20% rise followed by a 20% fall does not return you to the start. 100 rises to 120, then falls by 20% of 120 — which is 24, not 20 — leaving 96.
The reason is that each percentage is taken of a different base. To undo a 20% increase you need a 16.67% decrease; to undo a 50% loss you need a 100% gain. This asymmetry is behind a great deal of misleading statistics.
100 → +20% → 120 → −20% → 96
Percent versus percentage point
When the quantity is itself a percentage, the two are different. A rate moving from 2% to 3% has risen by one percentage point, but by 50% in relative terms.
Both statements are true and they describe very different magnitudes, which is why the distinction matters in reporting on interest rates, unemployment and election polling.
Frequently asked questions
How do I calculate a percentage decrease?
Subtract the new value from the old value, divide by the old value, then multiply by 100. From 100 to 80: (100 − 80) ÷ 100 × 100 = 20%.
Why does a 50% loss need a 100% gain to recover?
Because the gain is measured from the reduced base. Falling 50% from 100 leaves 50; returning to 100 means adding 50 to 50, which is a 100% increase.
Can a percentage decrease exceed 100%?
Not for a quantity that cannot go below zero — falling to zero is exactly 100%. A larger figure only makes sense where negative values are possible, such as a profit turning into a loss.
Is a 20% decrease the opposite of a 20% increase?
No. Applying both leaves you at 96% of the original, not 100%, because each percentage is taken of a different base. To reverse a 20% increase you need a 16.67% decrease.
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