Identify the two values: original (A) and new (B)
Compute the absolute difference: |B − A|
Add the two values: A + B
Compute the percent difference: (|B − A| ÷ ((A + B) / 2)) × 100
If A + B = 0, percent difference is undefined
If you need a simpler alternative (not percent difference): ((B − A) ÷ A) × 100 (percent change)