What Is Percent Change?
Percent change measures how much a quantity has grown or shrunk relative to its original size, expressed as a percentage. It is one of the most widely used calculations in finance, science, statistics, and everyday life — from tracking price increases to measuring growth in followers, weight, or sales.
How to Use This Calculator
Enter the old value (the starting or original amount) and the new value (the final or current amount). The calculator returns the percent change. A positive result indicates an increase; a negative result indicates a decrease. It also shows the absolute change (new − old) so you can see the raw difference at a glance.
The Formula Explained
The percent change formula is:
$$\text{Percent Change} = \frac{\text{New Value} - \text{Old Value}}{\text{Old Value}} \times 100\%$$
You subtract the old value from the new value to get the difference, divide that difference by the old value to normalize it against the starting point, then multiply by 100 to convert the ratio into a percentage. Dividing by the old value (not the new value) is what makes it a true "change relative to the starting point."
Worked Example
Suppose a stock rose from $50 to $75. The change is \(75 - 50 = 25\). Divide by the old value: \(25 \div 50 = 0.5\). Multiply by 100 to get 50%. So the stock increased by 50%.
Now suppose a price dropped from 80 to 60. The change is \(60 - 80 = -20\). Divide: \(-20 \div 80 = -0.25\), times 100 = −25%, a 25% decrease.
FAQ
Is percent change the same as percent difference? No. Percent change uses the old value as the reference (denominator), while percent difference uses the average of both values. Use percent change when one value clearly comes "before" the other.
What if the old value is zero? Percent change is undefined when the old value is zero, because you cannot divide by zero. This calculator returns 0 in that case to avoid an error.
Can the result be over 100%? Yes. If a value more than doubles, the percent change exceeds 100%. For example, going from 10 to 30 is a 200% increase.
