Discount Calculator
One discount or two stacked — they multiply rather than add, and this calculator proves it on your price — plus the saving, and the total with sales tax if you add it.
Percentages off do not add — they multiply
A 20% discount followed by an extra 10% off is not 30% off: the second percentage applies to the already-reduced price, yielding 28%. Retailers present the stacked version because intuition adds. This calculator multiplies, correctly, and states your true saving so the two can be compared in the open.
Sale price = original × (1 − first%) × (1 − extra%)
Example: $120 with 20% off, then an extra 10%: $120 → $96 → $86.40, a real saving of 28%. The sign said '30% total savings' in your head; the register — and this page — say $33.60 saved, not $36.
The tax order matters too
In most US jurisdictions sales tax is charged on the discounted price when the discount is the retailer's own (a store sale), but on the pre-discount price for manufacturer coupons in some states. The tax field applies to the discounted price here — the common case — and the label says so.
How this is calculated
Discounts apply sequentially: price × (1 − p1) × (1 − p2). Total effective discount = 1 − (1 − p1)(1 − p2), displayed so the addition fallacy is visible. Tax, when entered, multiplies the discounted price. Rounding is to cents at display, as a register would.
Frequently asked questions
Why do stores stack 'extra % off' instead of one bigger discount?
Because 20% + 10% feels like 30% and costs them 28% — the framing is the margin. Some also protect the headline price for future promotions. Either way, multiplication is your defense.
Is 'buy one get one 50% off' a 25% discount?
On two identical items, yes — total paid is 150% of one price for two items, a 25% average saving. On items of different prices the cheaper one is discounted, which is its own small lesson in reading offers.
Does the discount or tax come first?
For retailer discounts, almost everywhere the tax follows the discount. Manufacturer coupons are the exception in several states (tax on the full price). When the amounts matter, the receipt's arithmetic is the local law made visible.
How do I reverse a discount (find the original price)?
Divide the sale price by (1 − discount): $86.40 ÷ 0.72 = $120. With two stacked discounts, divide by both factors in turn — the percentage calculator's family handles the general shapes.
Embed this calculator
Writing about money — a blog, a school page, a community site? Put this calculator on your page, free: copy the code below and paste it where you want the calculator to appear. It stays up to date automatically — the small credit line underneath is all we ask in return.
CalcPrincipal