Percentage Decrease Calculator

Calculate percentage decrease from original to new value. Find the percent reduction between two numbers.

This calculator subtracts the New Value from the Original Value to get the raw Decrease, then divides that Decrease by the Original Value and multiplies by 100 for the percentage. Because the denominator is Original Value, the two inputs behave differently from each other: raising Original Value while New Value stays fixed pushes the Decrease up, since there is now more distance to fall, while raising New Value with Original Value fixed pulls the Decrease down, since the ending point has moved closer to the starting one. At the default figures of 100 falling to 80, Original Value carries a slightly larger measured influence over the reported Decrease than New Value does for a comparable proportional change, because a percentage nudge moves a field by an amount proportional to its own magnitude, and Original Value is the larger of the two numbers at the defaults — so it moves by more raw units than New Value does for the same percentage nudge. The formula assumes Original Value is not zero, since dividing by zero has no defined result; the engine reports a 0% change in that specific case rather than an error. Nothing in the calculation actually verifies that a decrease has occurred — enter a New Value larger than Original Value and it will still compute a signed negative Decrease and a negative Percentage Decrease, rather than switching over to describe the change as an increase or flagging that the direction of change does not match the calculator's name.