Percentage change = ((New value − Old value) / Old value) × 100
If the result is positive, it’s an increase
If the result is negative, it’s a decrease
If Old value = 0, percentage change is not defined
Example: from 50 to 65 → ((65 − 50) / 50) × 100 = 30%
Example: from 80 to 60 → ((60 − 80) / 80) × 100 = −25%