Percentage change calculator
Compare an old value with a new one to measure growth, decline, performance, price movement, or any other change.
● Your numbers stay in this browser.
(100 − 80) ÷ 80 × 100
From question to answer in three moves.
Enter the original value.
Enter the new value.
See the signed percentage change and difference.
The calculation is visible, not a black box.
The original value must not be zero. With a negative original value, the sign may be counterintuitive: −80 to −40 gives −50% although the value increases. Read the difference alongside the percentage.
Formula usedchange % = (new − original) ÷ original × 100
Calculation checks updated 27 September 2026: automated tests cover sample inputs and numeric boundaries, not every possible input or commercial rule.
Math without mystery.
What is the percentage change formula?+
Subtract the old value from the new value, divide the difference by the old value, then multiply by 100.
Why can’t the original value be zero?+
Percentage change divides by the original value, so a starting value of zero makes the standard formula undefined.
What does a negative result mean?+
With a positive original value, a negative result means a decrease. With a negative original value, the standard formula reverses this sign interpretation: from −80 to −40 gives −50% although the value rises. Check the difference and the values as well as the percentage.