Percentage change is always measured against the ORIGINAL value: (new − old) ÷ old. Dividing by the new value — or by the total, or by an average — gives a plausible-looking number that's simply wrong.
After computing the difference, your attention is on the most recent number you touched — usually the new value — so it feels natural to divide by it. Test writers know this and put the inverted answer among the options every time.
Before dividing, say (or write) which number is the base: "change FROM 2023" means 2023 is the base. If the question says "from A to B", A is the base — no exceptions. Sanity check: a rise from 100 to 150 must be +50%, not +33%.
| Year | Revenue (£m) |
|---|---|
| 2023 | 620 |
| 2024 | 760 |
By what percentage did Carraway plc's Revenue change from 2023 to 2024?
Percentage change = (new − old) ÷ old × 100. Always divide by the original (earlier) value. The correct answer is 22.6%. Traps to avoid: 20.3% comes from the "base as average" error; 10.1% comes from the "wrong base total" error; 122.6% comes from the "ratio not change" error; 18.4% comes from the "inverted base" error.
This trap appears in 36 of our questions, across: Percentage change · Margin change.
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