How to Calculate Percentage Decrease, Step by Step

Percentage decrease shows up everywhere -- a price drop, a pay cut, a weight-loss goal, a shrinking population. The formula is short, but it's also the one most people apply backwards when the numbers get swapped around. Here's the exact method, worked through with real numbers.

The Formula

Percentage decrease compares how much a value fell to the value it started at:

Percentage decrease = (Old Value − New Value) ÷ Old Value × 100

Worked Example

1. 1

   Write down the old and new values

   A jacket was $80 and is now $60. Old value = 80, new value = 60.

2. 2

   Subtract new from old

   80 − 60 = 20. That's the actual drop in dollars.

3. 3

   Divide the drop by the old value

   20 ÷ 80 = 0.25.

4. 4

   Multiply by 100 to get a percentage

   0.25 × 100 = 25% decrease.

When the Result Looks Wrong

If you divide by the new value instead (20 ÷ 60 = 33.3%), you'll get a bigger, wrong number. That 33.3% answers a different question -- "by what percentage would I need to increase $60 to get back to $80?" -- not "by what percentage did $80 decrease?" Keep the two straight by always anchoring the denominator to the starting value.

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Frequently Asked Questions

What if the new value is bigger than the old value?

Then it's a percentage increase, not a decrease -- the same subtraction (Old − New) just comes out negative, which is your signal to flip the formula around and divide by the old value for an increase calculation instead.

Does percentage decrease work the same way for negative numbers?

The formula still works, but interpreting it gets tricky with negative old values (e.g. a bank balance going from -$50 to -$100 is technically a "decrease" in value but an increase in debt) -- for anything involving negative numbers, it's safer to describe the change in plain dollars/units rather than a bare percentage.