What is the sign convention for percent change?
A positive sign (+) denotes an increase, while a negative sign (-) denotes a decrease. If old and new values are equal, the change is exactly 0%.
Why does going from 100 to 50 differ from going from 50 to 100?
Because the denominator changes. From 100 to 50 is a 50% drop (50/100). From 50 to 100 is a 100% gain (50/50).
Can percent change be calculated if the original value is negative?
Yes. The formula divides by the absolute value of the old number: (New - Old) ÷ |Old|. For example, moving from -10 to +10 is (10 - (-10)) ÷ 10 = +200%.
What happens when the old value is zero?
If the starting value is zero, percent change is mathematically undefined because division by zero cannot yield a finite number.
Is percent change the same as basis points?
One percentage point of change equals 100 basis points (bps). Percent change measures relative rate, whereas basis points measure absolute differences in interest rates.
How accurate is the result?
Results use JavaScript's 64-bit floating point — accurate to 15+ significant digits for most calculations.
Can I enter decimal numbers?
Yes, decimals are fully supported.
Is it free?
Yes, completely free.
Does it show the formula?
Yes, the formula is displayed on the page.
Can I use it on mobile?
Yes, the calculator is fully responsive.
Does it save my inputs?
No data is stored — all calculations are done locally in your browser.
What if I get an error?
Check for invalid inputs such as division by zero or negative square roots.