How to calculate percentage change
The formula:
% change = ((New − Old) ÷ Old) × 100
Worked examples
- Salary: R28,000 → R30,000.
((30,000 − 28,000) ÷ 28,000) × 100 ≈ +7.14%. - Petrol price: R23.50/L → R25.10/L.
((25.10 − 23.50) ÷ 23.50) × 100 ≈ +6.81%. - Investment: R100,000 → R85,000.
((85 − 100) ÷ 100) × 100 = −15%. - Exam improvement: 65% term 1 → 78% term 2.
((78 − 65) ÷ 65) × 100 = +20%.
Percentage change vs percentage point change
If a savings rate moves from 5% to 7%, that\'s a +2 percentage points change but a +40% percentage change (because 2 is 40% of 5). News headlines often confuse these two — the calculator above gives the percentage change interpretation.
Asymmetry between increase and decrease
A −20% drop followed by a +20% rise does not return you to the original. R1,000 → −20% → R800 → +20% → R960. To recover from a −20% drop you need a +25% rise. This matters for stocks, currencies, and any volatile value.