How do you calculate percentage change between two time periods?

• A. ((Value2 - Value1) / Value1) × 100, ensuring consistent units and handling missing data.
• B. (Value2 - Value1) × 100
• C. (Value1 - Value2) / Value1 × 100
• D. Value2 / Value1 × 100

Answer: (A)

Percentage change is how much something has changed relative to where it started, expressed as a percent. To work this out, find the difference between the final value and the initial value, then divide that difference by the initial value to normalise it, and finally multiply by 100 to convert to a percentage. This gives a positive result for an increase and a negative result for a decrease, and it naturally compares the change to the starting level.

Using the initial value as the baseline matters, and you must keep units consistent. If the initial value is zero, the percentage change is undefined, so you’d need a different approach or data.

The other options don’t capture the change relative to the starting point: simply multiplying the difference by 100 ignores the baseline; reversing the order would flip the sign; and converting the final value to a percentage of the initial value would give how large the final value is as a share of the start, not how much it changed.