Percentage change tells you how much a number grew or shrank relative to where it started. It is how price rises, revenue growth, traffic drops and discounts are usually reported. This calculator also shows the change it would take to return to the starting value, which is almost never the same percentage in reverse.
How it works
Subtract the starting value from the new value to get the difference. Divide that difference by the starting value, then multiply by 100. A positive result is an increase and a negative result is a decrease.
The starting value is always the base. That is why going from 80 to 100 is a 25% increase, while going from 100 back to 80 is a 20% decrease. The difference is 20 both times, but it is divided by a different base.
If the starting value is 0, percentage change is undefined, because you cannot divide by zero. The calculator shows n/a in that case.
A worked example
A price that rises from 80 to 100 has gone up by 20, which is a 25% increase (20 ÷ 80). To fall back to 80, it would need to drop by 20% (20 ÷ 100). The new price is 1.25 times the old one.
Questions people ask
What is the difference between percentage change and percentage points?
Percentage points measure the gap between two percentages by simple subtraction. If an interest rate goes from 4% to 5%, it rose by 1 percentage point, but by 25% in percentage change terms. News reports mix these up often, so it is worth checking which one is meant.
Why doesn't a 50% drop followed by a 50% rise get me back to where I started?
Because the second change uses a smaller base. 100 falls 50% to 50, and a 50% rise on 50 only adds 25, giving 75. To recover from a 50% drop you need a 100% rise. The "change needed to get back" result shows this for your numbers.
Can I use negative numbers?
Yes. The calculator divides by the size of the starting value, so a move from -50 to -25 shows as a 50% increase, since the number went up. For values that cross zero, such as profit turning into loss, percentage change can be hard to interpret, and the plain difference is often more useful.