Percentage Decrease Calculator

Find how far a value has dropped in percentage terms, or take a percentage off a number.

Percentage decrease between two values

Percentage decrease25%
Signed percentage change
−25%
Absolute change
−30

Working

  1. Difference: 90 − 120 = −30
  2. Divide by the original value: −30 ÷ 120 = −0.25
  3. Multiply by 100: −25%

Decrease a value by a percentage

80 decreased by 15%68
Amount of decrease
12

Working

  1. Decrease amount: 80 × 15 ÷ 100 = 12
  2. New value: 80 − 12 = 68
  3. Shortcut: 80 × 0.85 = 68

The percentage decrease formula

decrease % = (original − new) ÷ original × 100

original
the starting value
new
the reduced value

To reduce a number by p%, multiply it by (1 − p ÷ 100). Taking 15% off is the same as keeping 85%, so multiply by 0.85.

Worked example

A value falls from 120 to 90

  1. Drop: 120 − 90 = 30
  2. Divide by the original: 30 ÷ 120 = 0.25
  3. Multiply by 100: 25%

The value decreased by 25%.

Reduce 80 by 15%

  1. Keep 100% − 15% = 85%
  2. 80 × 0.85 = 68

80 reduced by 15% is 68.

Things to watch

  • A decrease can never exceed 100% if the value stays at or above zero; a 100% decrease means the value fell to zero.
  • Undoing a decrease needs a larger percentage increase: after a 25% drop from 120 to 90, you need a 33.33% rise to get back to 120.
  • For shop prices with more than one discount, use the discount calculator — stacked discounts multiply rather than add.

Typical uses

Measuring a fall in energy use, a drop in error rates, reduced journey times, or how much a price has come down between two dates.