Black Friday 2026 falls on November 27, and the ads are already promising "extra 20% off already-reduced prices." Here is the uncomfortable truth that costs shoppers money every year: 30% off plus 20% off is not 50% off. It is 44% off. The second discount applies to the already-reduced price, not the original.

This guide shows you the exact math, the one formula that predicts any stack, and the tricks retailers use to make deals look bigger than they are. No guessing, no mental arithmetic at the register — just numbers you can check in seconds.

Try Percent Off Calculator — free, no sign-up, and it runs entirely in your browser.

Why 30% Off Plus 20% Off Is Not 50% Off

Percent-off discounts multiply, they don't add. When a store takes 30% off a jacket, you pay 70% of the price. When a second 20% coupon applies, it comes off the new price, not the sticker.

Original price: $100
After 30% off: $100 × 0.70 = $70
After extra 20% off: $70 × 0.80 = $56

You paid $56, so your total discount is $44 — 44% off, not 50%. The missing 6 percentage points are the "20%" that was calculated on the $30 you already saved, not on $100.

The bigger the first discount, the smaller the second one's real value. A 20% coupon stacked on a 70%-off clearance item saves you only 6 extra percentage points (you end up at 76% off).

The Stacked Discount Formula (One Line of Math)

To combine any two percentage discounts, multiply what you pay, not what you save:

Effective discount = 1 − (1 − a) × (1 − b)

Where a and b are the two discounts as decimals. Three discounts? Keep multiplying: 1 − (1−a)(1−b)(1−c).

Worked example for 25% + 30%:

(1 − 0.25) × (1 − 0.30) = 0.75 × 0.70 = 0.525
You pay 52.5%, so the effective discount is 47.5%

Running these by hand at the shelf is a pain, so use the Percent Off Calculator — it handles stacked discounts and adds sales tax to the final price in one step. For single discounts, the Discount Calculator shows savings and final price side by side.

Common Stack Combos, Decoded

Here is what popular two-discount stacks actually equal, so you never overestimate at the register:

20% + 20% → 36% off
25% + 25% → 43.75% off
30% + 30% → 51% off
20% + 25% → 40% off
30% + 20% → 44% off
40% + 20% → 52% off
50% + 20% → 60% off
70% + 20% → 76% off

Notice the pattern: the same "20% coupon" is worth 16 points on top of 20% off, but only 6 points on top of 70% off. Stacks only feel huge when the base discount is modest — which is exactly how clearance-plus-coupon deals get marketed.

Also note that order does not matter for two percentages: 30% then 20% equals 20% then 30%. Multiplication commutes. If a cashier insists the order changes the percentage outcome, it doesn't — but order does matter with fixed-dollar coupons, covered below.

Real Example: The $899 TV

Say a doorbuster TV is listed at $899 with 30% off, and your email coupon takes an extra 20%:

After 30% off: $899 × 0.70 = $629.30
After extra 20% coupon: $629.30 × 0.80 = $503.44
Total saved: $395.56 — an effective 44% off

Now add sales tax. At New York City's combined 8.875% rate, you actually pay $503.44 × 1.08875 = $548.12. In a state with no sales tax on the item (say, most groceries, or Delaware entirely), you'd pay the flat $503.44. The spread between high-tax and no-tax states on a big-ticket item can exceed $45 on this one purchase — worth factoring into "deal" comparisons across retailers.

Fixed-Amount vs Percent Coupons: Order Changes the Price

Unlike two percentages, mixing a fixed-dollar coupon with a percent-off coupon makes order matter — sometimes by real money:

Percent first, then $20 off: $100 → 30% off → $70 → minus $20 → $50
$20 off first, then percent: $100 → $80 → 30% off → $56

Applying the percentage before the fixed coupon wins here because the percent comes off the larger number. Most store systems apply them in one fixed order, and it is usually the one better for the store. Ask which order the register uses, or just test both in the calculator before you commit — on a $100 item the difference is $6; on a $500 cart it compounds to $30.

One more trap: "extra 20% off already-reduced items" is a stack (multiplicative, 44%-type math), while "20% off the original price" applied alongside a markdown can be additive. The wording difference is worth 6 percentage points on a 30% base.

How Sales Tax Changes the Final Number

Sales tax is calculated on the price after all discounts in nearly every US state — a legit stack lowers your tax bill too. That means the true value of a discount stack in a high-tax state is slightly bigger than the sticker math suggests.

Quick method for estimating your walk-out price:

Apply each percent discount in sequence (or use the formula above).
Subtract any fixed-dollar coupons last.
Multiply by (1 + your local sales tax rate).

The Percent Off Calculator does all three steps at once and shows the tax as a separate line, so you can compare a deal in your own state rather than the ad's national price.

Was/Now Price Checks: Catching Fake Discounts

Before treating a "50% off" badge as real, verify the anchor price. The math: discount % = (original − sale) ÷ original.

Tag says "was $199, now $129 — 40% off!"
Check: ($199 − $129) ÷ $199 = 0.352 → 35.2% off, not 40%

Retailers sometimes anchor to a brief inflated price or an MSRP nobody charged. Two practical defenses:

Compute the claimed percentage yourself. If the math doesn't match the sign, the sign is marketing, not information.
Track the price for a few weeks. If the "was" price only existed for two weeks in September, the discount is theater. Set a Countdown Timer to Black Friday on November 27 and check the price weekly in the run-up — a genuine doorbuster should be at or below its lowest fall price.

Gift Cards and Cashback: The Hidden Extra Percent

Two promos quietly stack on top of percentage discounts:

Gift card bonuses ("get a $50 gift card with a $300 purchase") are worth about 50 ÷ 350 ≈ 14.3% effective discount — but only if you would shop there again anyway. If you never redeem the card, the bonus is worth zero.
Cashback portals and rewards cards typically add 1–5%. Because cashback applies to your post-discount total, it multiplies with the discount stack rather than adding to it: a 44% stack plus 3% cashback lands you at roughly 45.7% total, not 47%.

Both are still free money — just keep expectations aligned with the multiplicative reality.

The 2026 Calendar to Plan Against

Black Friday: Friday, November 27, 2026
Cyber Monday: Monday, November 30, 2026
Online "early Black Friday" pricing typically starts 7–10 days earlier, and many retailers run the same stack twice — once early, once on the day. If the early stack hits the effective-discount number you want, buy; doorbuster inventory on the day itself is deliberately thin.

The play: decide your target effective discount before the ads hit (for example, "the TV at ≥45% off"), compute the dollar price that implies, and buy the first stack that reaches it. A Countdown Timer set to November 27 keeps the deadline visible without feeding you urgency you didn't choose.

FAQ

How do you calculate percent off? Multiply the price by (1 − discount). For $80 at 25% off: 80 × 0.75 = $60. For stacked discounts, multiply the payment factors together first — 25% off plus 30% off means paying 0.75 × 0.70 = 0.525, so 47.5% off.

Is 30% off plus 20% off equal to 50% off? No. It equals 44% off, because the second discount applies to the already-discounted price. The shortcut 1 − (1−0.30)(1−0.20) = 0.44 gives the effective discount for any pair of percentages.

Does the order of stacked discounts matter? Not between two percentages — 30% then 20% equals 20% then 30%. It does matter when you mix a fixed-dollar coupon with a percentage: applying the percentage to the full price before subtracting the fixed coupon almost always wins.

How does sales tax affect a Black Friday discount? Tax is charged on the post-discount price, so a bigger stack also shrinks your tax. A $503.44 post-discount TV costs $548.12 at NYC's 8.875% rate — budget for tax when comparing deals across states or retailers.

How do I check if a "was/now" discount is real? Divide the savings by the original price: (original − sale) ÷ original. If the sign says 40% but the math gives 35%, the anchor price is inflated — and if you can, verify the "original" price was actually charged for several weeks before the sale.