Percentage Increase vs Decrease
Both formulas compare a change to the original value. The difference is whether the value went up or down.
Percentage Increase
Use when the new value is greater than the old value (e.g. price went up, marks improved).
Formula: ((New − Old) ÷ Old) × 100
Example: Old price 50, new price 65. Increase = ((65 − 50) ÷ 50) × 100 = 30%.
Percentage Decrease
Use when the new value is less than the old value (e.g. discount, drop in score).
Formula: ((Old − New) ÷ Old) × 100
Example: Old price 80, new price 60. Decrease = ((80 − 60) ÷ 80) × 100 = 25%.
Summary
- Increase: new > old → use (new − old) / old × 100
- Decrease: new < old → use (old − new) / old × 100
- In both cases the denominator is the original (old) value.