To find a percentage decrease, subtract the new value from the original, divide by the original and multiply by 100. To decrease a number by a percentage, multiply it by 1 minus the percentage divided by 100: decreasing 150 by 20% gives 150 × 0.8 = 120.
Formulas
% decrease = (original − new) ÷ original × 100new value = original × (1 − % ÷ 100) Examples
- A laptop drops from 900 to 765: (900 − 765) ÷ 900 × 100 = 15% decrease.
- Take 30% off 250: 250 × 0.7 = 175.
Common mistakes
- Dividing by the new value. From 900 to 765 is a 15% decrease; dividing by 765 gives 17.6%, which is wrong.
- Expecting −20% and then +20% to cancel out: 100 → 80 → 96.
In Excel and Google Sheets
- Decrease from A2 to B2 (format as %)
=(A2-B2)/A2 - Decrease A2 by the % in B2
=A2*(1-B2)
FAQ
Can a percentage decrease be more than 100%?
Not for amounts that can’t go below zero. A 100% decrease already takes a value to 0.
How do I find the original value after a decrease?
Divide the new value by 1 minus the percentage: 120 ÷ 0.8 = 150. The reverse percentage calculator does it in one step.
Is a percentage decrease the same as a discount?
The math is the same. The discount calculator also shows how much you save and handles stacked discounts.
How we calculate: exact decimal math (no rounding errors), you choose the decimal places, and your numbers never leave your browser. Methodology →
Updated October 2026