Discount & Sale Calculator
Find out exactly how much you save on shopping deals, promo codes, stacked clearance sales, and sales tax.
Consumer Math: Stacked Discounts & Real Savings
How Stacked Discounts Actually Work
When a store advertises “20% off plus an extra 15% VIP coupon,” they are multiplicative, not additive (i.e. not 35% off).
On a $100 purchase: 20% off drops the price to $80. Then 15% off $80 is $12, giving a final pre-tax price of $68. The effective discount is 32%, saving you $32 instead of $35.
Taxable Amount After Discounts
In most jurisdictions, store-funded manufacturer or retailer discounts reduce the taxable subtotal before sales tax is calculated.
However, mail-in rebates or post-purchase cashbacks do not lower the sales tax owed at the checkout register.
Percentage Off Formula
To manually check any markdown:
Sale Price = Original - Savings
For rapid mental math: 10% is moving the decimal left one spot; double that for 20%, or cut in half for 5%.