PercentLab

Percent Increase / Decrease

Positive change vs. negative change — both sides.

Two framings of the same move

Going from 80 to 100 is a 25% increase, but going back from 100 to 80 is only a 20% decrease — the percentages aren't symmetric because the base you're dividing by changes direction.

Where this trips people up

Sale prices are the classic trap: a 50% price increase followed by a 50% decrease does NOT return you to the original price — it leaves you 25% below it.

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PercentLab

Percent Increase / Decrease

Positive change vs. negative change — both sides.

Original

New

Increase %

Decrease %: -25

What you entered

Original: 80New: 100

1
Difference
100 − 80= 20
2
As a % increase over the original
(20 ÷ 80) × 100= 25%
3
As a % decrease framing (reverse direction)
((80 − 100) ÷ 80) × 100= -25%

Result

Increase %: 25

From 80 to 100 is a 25% increase.

Two framings of the same move

Going from 80 to 100 is a 25% increase, but going back from 100 to 80 is only a 20% decrease — the percentages aren't symmetric because the base you're dividing by changes direction.

Where this trips people up

Sale prices are the classic trap: a 50% price increase followed by a 50% decrease does NOT return you to the original price — it leaves you 25% below it.