Percent change tells you how much something grew or shrank relative to where it started — the difference between 'grew by 10' and 'grew by 10%'.
The percent change formula
Percent change = ((New − Old) ÷ Old) × 100
The 'old' value is always the denominator — the original amount you started from.
How to calculate a percentage increase
- Subtract the old value from the new value.
- Divide the result by the old value.
- Multiply by 100 to express it as a percent.
A rise from 40 to 50: (50 − 40) ÷ 40 × 100 = 10 ÷ 40 × 100 = 25% increase.
How to calculate a percentage decrease
The same formula — the negative sign simply means a decrease:
A drop from 250 to 200: (200 − 250) ÷ 250 × 100 = −0.2 × 100 = 20% decrease.
Percentage points are not percents
A move from 5% to 7% is a rise of 2 percentage points, but the relative increase is (7 − 5) ÷ 5 × 100 = 40%. News headlines mix these up constantly — know which one you mean.
Why increases and decreases don't cancel
A 50% increase followed by a 50% decrease does not return to the start:
- 100 → +50% → 150
- 150 → −50% → 75
Percent changes compound because each one applies to a new base.
A worked example
Your electricity bill rose from $94 to $118: (118 − 94) ÷ 94 × 100 ≈ 25.5% increase.
Put it into practice
Run any increase or decrease instantly on the free Percentage Calculator.
