Revising percentage change the night before an exam? These are condensed revision notes — the facts, formulas and mistakes examiners actually mark, with no long explanations. Prefer a full walkthrough with step-by-step reasoning instead? Search “Percentage change GCSE” on the site for the complete guide.
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Key facts to remember
1Percentage change = (change ÷ original) × 100.
2A positive result is a percentage increase; negative is a percentage decrease.
3The original value is always the starting value — not the new one.
4Compound interest applies a percentage change repeatedly over multiple periods.
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Formulas
Percentage change
((New − Original) ÷ Original) × 100
Compound interest
Final = Principal × (1 + r/100)ⁿ
r = rate, n = number of periods
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Worked examples
Example 1
A jacket costs £80 and is reduced to £60. Find the percentage decrease.
Working
Change = 80 − 60 = 20
Percentage decrease = (20 ÷ 80) × 100
= 0.25 × 100 = 25%
Answer25% decrease
Example 2
£500 is invested for 3 years at 4% compound interest per year. Find the final amount.
Working
Multiplier = 1.04
After 3 years: 500 × 1.04³
1.04³ = 1.124864
500 × 1.124864 = £562.43
Answer£562.43
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Common mistakes
✗Dividing by the new value instead of the original value.
✗Using simple interest instead of compound interest when the question says "compound".
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Exam tips
✓Highlight the word "original" in the question — it's always the denominator.
✓For compound interest, use the multiplier raised to a power rather than calculating year by year.
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