How-to guides · 3 min read
Percentage Increase and Decrease: Formulas and Examples
The formula
Subtract old from new, divide by the old value, multiply by 100. A positive answer is an increase, a negative one a decrease.
80 → 100
- That is a percent increase.
Step-by-step working 3 steps
- 1Find the change
100 − 80 = 20
- 2Divide the change by the old value
20 ÷ 80 = 0.25
- 3Multiply by 100
0.25 × 100 = 25%
Finding the new value
New = old × (1 + change/100). A 15% rise on 240 gives 240 × 1.15 = 276; a 15% fall gives 240 × 0.85 = 204.
Why +25% then −25% does not cancel
Start at 100, add 25% to reach 125, then take 25% off 125 to get 93.75. The multipliers 1.25 × 0.75 = 0.9375, not 1. To undo +25% you need −20%: 1.25 × 0.8 = 1.
The net change after +25% then −25%
- That is a percent decrease.
Step-by-step working 3 steps
- 1Find the change
93.75 − 100 = −6.25
- 2Divide the change by the old value
−6.25 ÷ 100 = −0.0625
- 3Multiply by 100
−0.0625 × 100 = −6.25%
Percent vs percentage points
A rate that moves from 10% to 12% rose by 2 percentage points but by 20% in relative terms. Use the percentage change calculator for either question.
Frequently asked questions
How do I calculate percentage decrease?
Use the same formula: (new − old) ÷ old × 100. The result is negative for a decrease.
Can a percentage increase exceed 100%?
Yes. Doubling is a 100% increase and tripling is 200%.
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