Why 40% off plus 20% off is not 60% off
Stacked discounts multiply instead of add. The second discount applies to the already reduced price:
- $120 × (1 − 0.40) = $72 after the 40% sale.
- $72 × (1 − 0.20) = $57.60 after the extra 20%.
- Total discount = 1 − (0.60 × 0.80) = 52%, not 60%.
Quick stacked-discount table
| Sale | + extra 10% | + extra 15% | + extra 20% | + extra 25% |
|---|---|---|---|---|
| 20% off | 28.0% off | 32.0% off | 36.0% off | 40.0% off |
| 25% off | 32.5% off | 36.3% off | 40.0% off | 43.8% off |
| 30% off | 37.0% off | 40.5% off | 44.0% off | 47.5% off |
| 40% off | 46.0% off | 49.0% off | 52.0% off | 55.0% off |
| 50% off | 55.0% off | 57.5% off | 60.0% off | 62.5% off |
| 60% off | 64.0% off | 66.0% off | 68.0% off | 70.0% off |
Is sales tax charged on the original or discounted price?
In most U.S. states, sales tax is calculated on the price you actually pay after store discounts. Manufacturer coupons can be treated differently in some states, so the calculator applies tax to the final discounted price as an estimate. For local rates, use the sales tax calculator.
Smart Black Friday checks
- Compare the deal price with the price from a few weeks earlier, not the “original” price on the tag.
- Add shipping, fees, and tax before comparing stores.
- Check return windows and price-match policies for holiday purchases.
More tips in our Black Friday 2026 discount math guide.
Discount Calculator with Tax FAQs
How do I calculate a discount?
Multiply the price by the discount percentage and divide by 100 to get the savings, then subtract it. 25% off $80 is $20 off, so you pay $60 before tax.
How do I calculate two discounts together?
Apply them one at a time. Multiply the price by (1 − first discount) and then by (1 − second discount).
Is it better if a coupon is applied before or after the percent discount?
For the shopper, a fixed-dollar coupon is usually worth more when it is applied after the percent discounts, because its full value comes off the final price. The store decides the order; use the setting above to compare both.
When is Black Friday 2026?
Black Friday 2026 is Friday, November 27, 2026, the day after Thanksgiving (Thursday, November 26). Cyber Monday is November 30, 2026.