Why 'extra 20% off' is not really 20%
Retailers love stacked discounts because the second one applies to the ALREADY-REDUCED price. An extra 20% off a 50%-off item is only 10% off the original — so the combined discount is 60%, not 70%.
- • $100 → 50% off = $50
- • Then extra 20% off $50 = $40
- • Total: 60% off $100, not 70%
Sales tax on discounts
In most US states, sales tax is calculated on the DISCOUNTED price (what you actually pay). A few states (CA, NY, TX) apply tax on the original price for manufacturer coupons but not store coupons — this calculator assumes the more common post-discount tax.
When % off beats $ off (and vice versa)
Percent-off wins on high-ticket items ($1,000 laptop: 20% off = $200 saved). Dollar-off wins on low-ticket ($15 candle: $5 off = 33% effective). Always convert to the same unit before comparing.
FAQ
How do I calculate 25% off $120?
$120 × 0.25 = $30 discount. $120 − $30 = $90 sale price. Add sales tax on the $90.
How do stacked coupons work?
The second coupon applies to the already-reduced price. 30% off, then extra 10% off = 37% total off (0.7 × 0.9 = 0.63), not 40%.
Is sales tax on the original or discounted price?
In most US states, tax is on the discounted price you actually pay. Some states tax the original price when a MANUFACTURER coupon is used but not for store discounts.
How much is 70% off $299?
$299 × 0.7 = $209.30 off. Sale price = $89.70 before tax.
What's 50% off plus 20% off?
60% off total, not 70%. The 20% applies to the already-halved price: $100 → $50 → $40.
How do I calculate percent off in reverse?
If sale is $75 and original was $100: (100 − 75) ÷ 100 = 25% off.
Do coupon exclusions matter?
Yes. Most stores exclude gift cards, some brands, and clearance from percent-off coupons. Read the fine print before assuming the discount applies.
What's the biggest discount ever legal?
There's no legal cap in the US, but 'up to X% off' claims must be supported by real prior pricing. FTC pricing rules require the 'was' price to have been the actual selling price recently.
How this calculator is built
Independently maintained
Written by Sam Doshi and the RevenueLab editorial team. We don't sell the data feeds this tool is built on.
Sourced from primary data
Benchmarks come from public AdSense / Stripe / IRS disclosures and reader-submitted data — never third-party "$X per view" claims. Full methodology.
Last reviewed
July 2026. We re-check every figure on the platform on a rolling quarterly cycle.
Editorial standards
See our editorial policy and disclaimer. Results are estimates, not advice.