Reverse Calculators
Percentage Change Calculator
Enter an old and new value to see the percentage change and absolute difference.
Percentage change
Percentage change answers how much a value rose or fell relative to where it started — wages, traffic, prices, grades or inventory. The usual formula is ((new − old) ÷ old) × 100. Sign matters: a fall is negative. People often subtract percentages of different bases and get nonsense; this tool keeps the base explicit. For finding an original after a known change, see reverse percentage and reverse discount. Stacked promotional cuts are not simple percentage changes — use discount stacking. Year-on-year business metrics should use comparable periods without one-off spikes unless you call them out. A 50% fall followed by a 50% rise does not return you to the start; run each step from its own base if you need the true path. Illustrative arithmetic only — not investment performance advice. Write the old and new figures beside the percentage so teammates can audit the step in a board pack.
Worked example
Price rises from £40 to £50: change = (50 − 40) ÷ 40 × 100 = 25%. A fall from £50 to £40 is −20%, not −25% — the base changed. Traffic from 8,000 to 10,000 visits is a 25% increase; from 10,000 back to 8,000 is a 20% decrease.
Limits and assumptions
Uses a single old/new pair. Compound growth across many periods needs a chain or CAGR formula. Not investment advice.
Frequently asked questions
How is percentage change calculated?
(New − old) ÷ old × 100. Use the original value as the denominator.
Why is a rise and fall asymmetric?
Because the base changes. Up 25% then down 20% can return to the start from £40 → £50 → £40.
Can the result exceed 100%?
Yes — values can more than double. That is a >100% increase.
What if the old value is zero?
Percentage change is undefined; describe the absolute change instead.
Percentage points vs percent?
A rate moving from 10% to 12% is a 2 percentage point rise, which is a 20% relative change.