Percentage Decrease Calculator
Calculate a drop in percent: enter the original value and the new, lower value.
About this tool
A percentage decrease expresses a fall relative to the starting value: it is the change between the two values, (new − old) ÷ |old| × 100, read with its sign — for 100 → 80 that is −20%, a 20% decrease. It powers discount maths, weight-loss tracking, traffic and price-drop reporting — anywhere the question is “how much did it go down, relatively?”
Enter the original and the new value; you get the signed percentage plus the raw difference. Remember the asymmetry this reveals: after a 50% decrease, you need a 100% increase to get back — the calculator linked in the related tools shows both directions.
How to use it
- Enter the original value in “From”.
- Enter the new value in “To”.
- Read the result: a negative percentage is the decrease (−20% means a 20% decrease); the note under it states the difference in plain words.
Frequently asked questions
How is percent change calculated?
Percent change = (new − old) ÷ |old| × 100. Dividing by the original value is what makes it a relative change: going from 80 to 100 is +25%, and going back from 100 to 80 is −20% — the two directions are not mirror images.
Can a decrease exceed 100%?
Only when the value falls below zero: 100 → −50 is a 150% decrease. As long as the new value stays at or above zero, a decrease cannot pass 100% — a 100% decrease means the value reached zero.
How do I calculate a discount percentage?
Divide the amount saved by the original price: $30 off $120 is a 25% decrease — or enter 120 and 90 above. The Discount Calculator works it from the sale side.