Math
How to subtract a percentage from a number
Subtract a percentage to calculate discounts, reductions and lower target values without mixing up the base.
Direct formula
To reduce a number by p percent:
new value = original value x (1 - p / 100)Reducing 800 by 15%:
800 x (1 - 0.15) = 800 x 0.85 = 680You can also calculate the reduction first—800 x 0.15 = 120—and subtract it from 800.
Common multipliers
| Reduction | Multiply by |
|---|---|
| 10% | 0.90 |
| 20% | 0.80 |
| 25% | 0.75 |
| 40% | 0.60 |
| 50% | 0.50 |
The original value is the base. A 20% reduction followed by a 20% increase does not return to the starting value: 100 x 0.80 x 1.20 = 96.
Subtracting a percentage from one value is different from measuring the percentage decrease between two known values. For the latter, use percentage decrease.
Use the percentage calculator in subtraction mode to verify a result.