What the percentage change calculator does
Enter an original value and a new value, and the calculator tells you the percentage increase or decrease between them. It is the calculation behind price rises, salary increases, sales growth, weight loss, investment returns and inflation — and it is easy to get backwards, because a 50% increase followed by a 50% decrease does not bring you back to where you started.
The formula
Percentage change = (new − original) ÷ original × 100
Price rose from $80 to $100: (100 − 80) ÷ 80 × 100 = +25%
Price fell from $100 to $80: (80 − 100) ÷ 100 × 100 = −20%
Followers went from 1,250 to 1,600: (1,600 − 1,250) ÷ 1,250 × 100 = +28%The denominator is always the original value — the one you are changing from. That is why the same $20 difference is 25% one way and 20% the other: it is measured against a different base.
Increase and decrease are not symmetric
| Loss | Gain needed to recover |
|---|---|
| −10% | +11.1% |
| −20% | +25% |
| −25% | +33.3% |
| −50% | +100% |
| −75% | +300% |
| −90% | +900% |
A stock that halves needs to double to get back to even. This asymmetry is why investors care so much about avoiding large drawdowns, and why a “20% off, then 20% on” sequence leaves a price 4% below where it started.
Percentage change vs percentage points
When the values themselves are percentages, be careful with wording. If an interest rate goes from 4% to 5%, that is a rise of 1 percentage point but a 25% increase in the rate. News reports mix these up constantly; the calculator gives the percentage change, so for rates, unemployment figures or poll numbers, decide which one you actually mean before quoting it.
Applying a percentage change
New value = original × (1 + change)
$80 with a 25% increase: 80 × 1.25 = $100
$100 with a 20% decrease: 100 × 0.80 = $80
Two rises of 10%: × 1.10 × 1.10 = × 1.21 (21%, not 20%)
Reverse: original = new ÷ (1 + change)
$100 after a 25% rise started at 100 ÷ 1.25 = $80Successive changes multiply, they do not add. Three years of 5% growth is 1.05³ = 1.158, a 15.8% total — the compounding that the Compound Interest Calculator explores in detail.
Common uses
- Pay rises: from $52,000 to $55,000 is +5.8%. Compare with inflation to see the real change.
- Sales and traffic: month-over-month or year-over-year growth — always compare like periods.
- Prices: checking a “was/now” label, or how much a bill has gone up.
- Health and fitness: weight, body-fat or lifting-total changes as a percentage rather than raw units.
- Investments: return over a holding period, before considering time (annualised return needs the compound formula).
- Science: percent error is |measured − true| ÷ true × 100 — the same formula with the accepted value as the base.