Percentage Change Calculator

How percentage change works

We use the standard starting-value convention:

(new − original) ÷ original × 100

From 80 to 100: (100 − 80) ÷ 80 × 100 = +25%, an increase. From 100 to 80: (80 − 100) ÷ 100 × 100 = −20%, a decrease. An unchanged value gives 0%.

Zero and negative starting values

An original value of zero makes this formula undefined. With a negative original, the percentage sign can run opposite to the numeric direction: −100 to −50 gives −50%, even though the new number is higher. The result shows both the formula sign and the numeric direction. We do not silently switch to an absolute denominator.

Precision & limits

Use a decimal point, no commas. Scientific notation is accepted. Absolute inputs may be up to 1 trillion; nonzero inputs must be at least 1e-12 in magnitude. Results display up to 12 significant digits; floating-point rounding can occur. This calculator measures change from a starting value, not percentage difference between two peers.