Percentage Change Calculator
Instantly find how much a value has grown or shrunk between two points. Use it to track price shifts, population changes, or any before-and-after comparison.
About this calculator
Percentage change measures how much a value has moved relative to its starting point. The formula is: Percentage Change = ((new_value − old_value) / |old_value|) × 100. Dividing by the absolute value of the original ensures the result is meaningful even when the starting value is negative. A positive result means an increase; a negative result means a decrease. For example, a stock rising from $50 to $75 represents a +50% change, while a drop from $75 to $50 is approximately −33.3%. This asymmetry is important — a 50% gain does not cancel out a 50% loss.
How to use
Suppose a product's price rose from $80 to $100. Enter 80 as the Original Value and 100 as the New Value. The calculator computes: ((100 − 80) / |80|) × 100 = (20 / 80) × 100 = 25%. The price increased by 25%. Now try a decrease: if the price fell from $80 to $60, the result is ((60 − 80) / 80) × 100 = −25%, confirming a 25% drop.
Frequently asked questions
What is the difference between percentage change and percentage difference?
Percentage change is directional — it compares a new value to a specific original value, showing growth or decline. Percentage difference, on the other hand, treats both values symmetrically by comparing their absolute difference to their average. Use percentage change when one value clearly came before the other in time, and percentage difference when neither value is a reference baseline.
How do you calculate percentage change when the original value is negative?
When the original value is negative, you still divide by its absolute value to avoid sign confusion. For example, if a temperature changed from −20°C to −10°C, the calculation is ((−10 − (−20)) / |−20|) × 100 = (10 / 20) × 100 = 50%, a 50% increase. The absolute value in the denominator ensures the direction of change is captured correctly in the numerator alone.
Why does a 50% increase followed by a 50% decrease not return to the original value?
Because each percentage is calculated on a different base. Starting at 100, a 50% increase gives 150. A 50% decrease from 150 gives 75 — not the original 100. This asymmetry is fundamental to percentage arithmetic and is why percentage change is always relative to the starting point, not a symmetric measure between two values.