Percentage Change Calculator

Percentage change expresses the difference between an old value and a new value relative to the old value. The formula is (new - old) / old times 100 percent. It answers not only how much a value changed, but how large that change was compared with where it started.

A rise from 10 to 15 and a rise from 1,000 to 1,005 are both increases of 5 units, but their percentage changes are very different. Percentage change gives scale to the comparison.

Positive percentage change indicates an increase from the baseline. Negative percentage change indicates a decrease. The baseline is essential. Changing from 50 to 100 is a 100 percent increase, while changing from 100 to 50 is a 50 percent decrease. The path is reversible in values but not symmetric in percentage terms.

This asymmetry surprises people. A 50 percent loss requires a 100 percent gain to return to the original value. Percentage changes should always be read with the starting value in mind.

Percentage change is undefined when the starting value is zero because division by zero has no meaning. When the baseline is very small, percentage changes can look enormous even if the absolute change is modest.

This is common in early-stage metrics. Growing from 1 customer to 3 customers is 200 percent growth, but it is still only 2 customers. Reporting should pair percentage change with absolute change so readers can judge scale.

Percentage change is useful for prices, KPI trends, traffic, costs, conversion rates, and scientific measurements. It becomes misleading when baselines are cherry-picked, negative values are involved without explanation, or the absolute scale is hidden.

Good reporting states the old value, new value, absolute change, percentage change, and time period. That gives the percentage enough context to be informative rather than dramatic.