Percentage change: why the starting value matters
An extra 60 orders can be a major jump for a small shop and a minor movement for a larger one. Percentage change puts that difference in context: the original amount matters as much as the difference.
Compare the new amount with the old amount
Percentage change = (new − old) ÷ old × 100. With a positive starting value, a positive result means an increase and a negative result means a decrease. Swapping the inputs changes the denominator, not just the sign.
Compare like with like: a full month with a full month, or the same package size before and after a price change. Correct arithmetic cannot repair a mismatched comparison.
References: BLS — Calculating percent changes
Percentage points answer a different question
A success rate moving from 4% to 5% has increased by 1 percentage point and by 25% relative to its earlier level. The first describes the movement of the rate; the second describes that movement relative to its starting value.
Include both endpoints when communicating a result. “From 4% to 5%” is harder to misread than “up 25%” on its own.
When the percentage stops being useful
A zero starting value makes the usual calculation undefined. Say “from 0 to 12” rather than inventing a 100% increase. For a change from a loss to a profit, state the amounts and the difference: a signed percentage can obscure what actually improved.
Successive changes cannot simply be added. Moving from 80 to 100 is a 25% increase; moving back to 80 is a 20% decrease because the second starting point is larger.
Worked example: reading order growth
Suppose a fictional shop records 240 orders and then 300 over equal-length periods. The increase is 60; 60 ÷ 240 = 0.25, or 25%. These are illustrative figures, not measurements from a real shop or website.
If orders later fall from 300 to 240, the change is −60 ÷ 300 = −20%. Keeping the original counts beside the percentage explains why the reversal is not a 25% decrease.