Percentage change calculator
Find the percentage increase or decrease between any two numbers — prices, scores, populations, traffic, anything that moves over time. Enter the original value and the new value, and the calculator returns the percentage change along with the absolute difference, so you can see both the relative and the actual change at once.
How it works
The calculator uses the standard percentage-change formula, dividing by the absolute value of the original so the sign reflects direction:
percentage change = (new − original) ÷ |original| × 100
absolute change = new − originalA positive result is an increase, a negative result is a decrease. The result is undefined when the original value is zero, because there is no baseline to compare against.
Example
Original 80, new 100:
- Absolute change: 100 − 80 = +20
- Percentage change: 20 ÷ 80 × 100 = +25% (an increase)
Reverse it — from 100 down to 80 — and the change is −20 ÷ 100 × 100 = −20%.
| Original | New | Change |
|---|---|---|
| 80 | 100 | +25% |
| 100 | 80 | −20% |
| 50 | 150 | +200% |
Common mistakes to avoid
Confusing percentage change with percentage points. If a loan rate rises from 3% to 4%, that is a 1 percentage-point increase, but it is a 33% increase in the rate itself. The formula above measures the relative change; when comparing two percentages directly, decide which meaning fits the context before reporting.
Swapping original and new. The denominator is always the original (starting) value, not the new one. Dividing by the wrong number inverts the relationship and gives a different — and wrong — result. For example, the increase from 80 to 100 is +25%, but dividing by 100 instead gives +20%, which is the decrease from 100 back to 80.
Expecting symmetry. A 25% increase followed by a 25% decrease does not return to the starting value — after 100 → 125 → 93.75, you end up below where you started. Percentage changes compound on different bases, so they do not cancel neatly.
Interpreting a change from a negative base. When the original value is negative, the formula still works — a loss narrowing from −$100 to −$60 is a +40% change. But the direction word (“increase”) can be counter-intuitive; always show the absolute values alongside the percentage to avoid confusion.
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