How to Calculate Percentage Decrease
Determining a percentage reduction helps in calculating discounts, loss of metrics, or performance declines. To work it out, you evaluate the drop relative to the starting original amount, then express that drop as a share of the original rather than of the new, smaller figure. This distinction matters: a $20 drop from $80 is a 25% decrease, but the same $20 rebuilt back onto $60 would be a 33% increase — percentage change is never symmetric.
When Would I Use a Percentage Decrease?
- Store discounts: Finding out how much cash you save on discounted markdown prices, and comparing which of two competing sales actually saves more money.
- Loss of metrics: Measuring drop rates in website visitors, churn rates, or carbon footprint declines month over month.
- Asset depreciation: Calculating value decrease in laptops, cars, and other physical gear for insurance, resale, or tax write-off purposes.
Worked Example: Sale Price
If a product's price falls from $80 to $60:
- Difference: 80 - 60 = 20
- Divide by original price: 20 / 80 = 0.25
- Multiply by 100: 0.25 × 100 = 25% decrease.
Second Example: Weight Loss
Suppose someone weighing 90 kg drops to 81 kg after a training program:
- Difference: 90 - 81 = 9
- Divide by starting weight: 9 / 90 = 0.10
- Multiply by 100: 0.10 × 100 = 10% decrease.
Percentage Decrease FAQ
Q: How do I calculate percentage decrease in Excel?
Use the formula =(OldValue-NewValue)/OldValue in an empty cell, and then set the cell formatting to percentage.
Q: What is the difference between percentage decrease and discount rate?
They are math equivalents. The discount rate represents the decrease percentage applied to the original retail price tag.
Q: Can percentage decrease be more than 100%?
No, if a positive value drops to zero, that is a 100% decrease. You cannot decrease past zero for absolute physical quantities.
Q: If a value drops 20% one month and 10% the next, is the total decrease 30%?
No. Successive percentage decreases compound rather than add. A $100 value that falls 20% becomes $80, and a further 10% drop takes it to $72 — an overall decrease of 28%, not 30%.