What this calculator does
The Black Friday Calculator turns an advertised deal into the number that actually matters: what you pay at the register. Enter the original (list) price, the headline discount, an optional coupon that stacks on top of the sale, and your local sales tax. The tool returns the final checkout price, the total dollars saved, the true combined percent off, and the sale price before tax so you can compare offers on equal footing.
The formula
Percentage discounts that stack are applied one after another, so they multiply rather than add:
- Sale price (before tax): Original × (1 − discount/100) × (1 − coupon/100).
- Total savings: Original price − sale price before tax.
- Effective discount: savings ÷ original price × 100 — the real combined percent off.
- Final price: sale price × (1 + tax/100), adding sales tax on the discounted amount.
The key thing to notice is that a 30% sale followed by a 10% coupon is not 40% off. It is 1 − (0.70 × 0.90) = 0.37, or 37% off. Stacked percentages always come out a little lower than their sum. Leave the coupon at 0 if only one discount applies, and set sales tax to 0 to see the pre-tax total.
Interpreting the output
The final price is the highlighted figure — the amount you hand over at checkout, tax included. Total savings and effective discount tell you how good the deal really is once the coupon and any "up to" marketing language are stripped away. Compare the effective discount across competing offers rather than trusting the biggest advertised percentage.
Using it well
- Enter the true original price, not a previously inflated "was" price, so the savings figure is honest.
- Only stack a coupon in the second field if the retailer actually allows it on top of the sale — many exclude sale items.
- Check whether your discount applies before or after tax; this tool follows the standard order of discount first, then tax.