How to Calculate Percentage Change (Increase and Decrease)
Percentage change answers one question: how big was the move, relative to where it started? That last part — relative to the start — is where every common mistake lives.
The formula
(New − Old) ÷ Old × 100. The result is positive for an increase, negative for a decrease. Going from 50 to 65: (65 − 50) ÷ 50 × 100 = +30%. Going from 65 back to 50: (50 − 65) ÷ 65 × 100 = −23.1% — not −30%, because the base changed.
| Scenario | Calculation | Result |
|---|---|---|
| Rent £1,200 → £1,320 | 120 ÷ 1,200 × 100 | +10% |
| Price £80 → £60 | −20 ÷ 80 × 100 | −25% |
| Followers 2,400 → 3,000 | 600 ÷ 2,400 × 100 | +25% |
| Salary £32,000 → £35,200 | 3,200 ÷ 32,000 × 100 | +10% |
When the starting value is negative
The plain formula misbehaves if you start below zero. A balance moving from −£50 to £50 has clearly improved, but dividing by −£50 makes the result come out as −200%, labelling a rise as a fall. The usual fix is to divide by the magnitude of the starting value — |Old| rather than Old — so the sign tracks the direction of the move: (50 − −50) ÷ 50 × 100 = +200%. The calculator does this, which is why it can disagree with a spreadsheet on negative starting figures.
Where the starting value is exactly zero, no percentage exists at all: any increase from nothing is an infinite proportion of it. Report the absolute change instead — “up 12 units from zero” — rather than a percentage.
The asymmetry trap
A 50% fall followed by a 50% rise does not return you to the start: 100 → 50 → 75. Each change applies to its own base, and the second base is smaller. This is why an investment that drops 50% needs a +100% gain just to break even — a fact worth internalizing before reading any market headline.
Reversing a change: finding the original
If a price is £66 after a 10% increase, the original was 66 ÷ 1.10 = £60 — not 66 minus 10%. Divide by (1 + rate) to undo an increase, by (1 − rate) to undo a decrease. This is the calculation VAT-inclusive prices need, and the one most people get wrong by subtracting.
Doing it fast
Anchor on 10% (move the decimal), then scale: a change of 6 on a base of 120 — 10% would be 12, so 6 is 5%. For anything that doesn’t divide neatly, the percentage change calculator gives the signed result and absolute difference live, and the general percentage formulas guide covers the other two percentage questions.
Questions people ask
Can percentage change be more than 100%?
Yes — going from 40 to 100 is a +150% change. Anything more than doubling exceeds +100%. Decreases, however, bottom out at −100% (reaching zero).
What’s the difference between percentage change and percentage points?
If a rate moves from 10% to 12%, that’s a change of 2 percentage points — but a 20% percentage change. News reports mix these up constantly.