How to calculate percentage change

Calculation is only half the job. The other half is defending which observation counts as original. Operations teams often anchor on the earliest period in a comparison, finance teams on fiscal year start, and product teams on launch week. Document the anchor once, then follow the same steps every reporting cycle.

Once the anchor is fixed, percentage change is a deterministic function of the two numbers. That predictability is why auditors like the formula: anyone can recompute it.

Use ((N − O) ÷ |O|) × 100% with O as the baseline and N as the updated measurement. The bars around O mean absolute value. If your tool omits them, negative originals can flip signs in confusing ways.

If you work entirely inside spreadsheet percent formats, remember whether 0.15 means fifteen percent or fifteen percentage points of a rate. Consistency beats clever formatting.

1. Freeze the baseline value as O.
2. Capture the new reading as N after the event.
3. Compute N − O and note the sign verbally (up or down).
4. Divide by |O|. If O is zero, stop and choose another story.
5. Multiply by one hundred and compare to quick checks (double/halve).
6. Round for display and record the rounding rule in footnotes if needed.

For large tables, consider logging both absolute and relative columns so downstream charts can switch views without recomputing.

Weekly active users move from 12000 to 13500. The difference is 1500. One thousand five hundred divided by 12000 is 0.125, so growth is +12.5% versus the prior week. Mention that the window is seven days so nobody annualizes the figure by mistake.

For more scenarios, see percentage change examples and the increase-focused article when the sign is positive.