๐ท๏ธ Stacked Discount Calculator
For sales like "20% off, then an extra 10% off", this tool calculates the final price and the true effective discount rate when discounts are applied in stages. Since discounts don't simply add up, this shows you exactly what stacking them really means.
How to use
- Enter the original price.
- Enter each discount rate in the order it's applied (use "Add discount step" to add more).
- The effective discount rate, total discount amount, and final price are calculated automatically.
How the calculation works
When discounts stack, each one applies to the price after the previous discount, not to the original price. That is why discount percentages cannot simply be added together. Applying a% off and then b% off to a price P gives a final price of P ร (1 โ a/100) ร (1 โ b/100). "20% off, then a further 10% off" is P ร 0.8 ร 0.9 = P ร 0.72, an effective discount of 28%. It is two points less than the 30% you might expect because the second 10% applies to an already reduced price, 80% of the original. Because the final price is a product, the order of the discounts does not matter: 0.8 ร 0.9 and 0.9 ร 0.8 are both 0.72.
Worked example
An 8,000 item with 30% off, a further 20% off, and a 10% member discount 1. 30% off: 8,000 ร 0.7 = 5,600 2. A further 20% off: 5,600 ร 0.8 = 4,480 3. Member 10% off: 4,480 ร 0.9 = 4,032 The final price is 4,032, an effective discount of 1 โ 0.7ร0.8ร0.9 = 0.496, or 49.6%. The percentages add up to 60%, yet the result does not even reach half price.
Things to be aware of
- This assumes each discount applies to the previous price in turn. Some retailers instead add discounts together against the list price, so check the terms.
- Fixed-amount discounts ("5 off") give different results depending on order. This tool handles percentage discounts only.
- Whether a discount applies before or after sales tax also changes what you pay.
- Rounding of fractions of a unit varies by store, so the actual charge may differ by a small amount.
FAQ
Does 20% off plus 10% off equal 30% off?
No. Each discount is applied to the price remaining after the previous discount, not to the original price, so 20% + 10% stacked works out to an effective 28% off.
Does the order of the discounts change the result?
No โ multiplication is commutative, so the final price is the same regardless of the order the discounts are applied in.
How many discount steps can I stack?
You can add up to 5 discount steps.