Black Friday Deals: Is It a Real Discount? (Free Maths)
Work out the real % off, why stacked coupons don't add up, and how to check "was" prices before Black Friday deals, with a free percentage calculator.
Published · 5 min read
Black Friday deals are only as good as the maths behind them. Before you buy, check three things: the real percentage off (saving ÷ original price × 100), what stacked coupons actually add up to (multiply, don't add), and whether the "was" price is the price the item really sold at. A "30% off" tag on a price that went up last month can save you almost nothing. The free percentage calculator checks each one in seconds.
In 2026, Black Friday falls on 27 November, the day after US Thanksgiving, with Cyber Monday on 30 November. Many shops in India, the UK and elsewhere now run their own sales on the same weekend, and some start a week or more early.
1. Find the real percentage off
Price tags often round in the shop's favour, or show only a "was" and "now" with no percentage at all.
Formula: (was − now) ÷ was × 100
Example: was $129.99, now $89.99.
- Open the calculator's third line, Percentage change (increase or decrease).
- Type 129.99 in From and 89.99 in to.
- It shows "A decrease of 30.7716% (−40)". That's about 31% off, and $40 saved.
Do this for two or three similar products and the best deal is often not the one with the biggest red sticker.
2. Stacked discounts multiply, they don't add
"30% off, plus an extra 15% with code" sounds like 45% off. It isn't, because the second discount comes off the already-reduced price.
Example on a $150 jacket:
- After 30% off: you pay 70%, so $105
- After an extra 15% off: you pay 85% of $105 = $89.25
- Total saving: $60.75, which is 40.5%, not 45%
The shortcut: multiply what you pay at each step. 0.70 × 0.85 = 0.595, so you pay 59.5% and save 40.5%.
The same goes for Indian sale-plus-bank-offer deals. A ₹4,999 pair of headphones at 40% off is ₹2,999.40. An extra 10% instant bank discount takes it to ₹2,699.46: a total of 46% off, not 50%. Bank offers also often have a minimum spend and a cap on the discount (for example, "up to ₹1,500"), so read the terms before counting on the full 10%.
3. Check the "was" price
A discount is only meaningful if the original price is real. Some ways a deal can look better than it is:
- The price went up before the sale. An item that sold for $99 all year is listed at $139 in October, then "30% off" on Black Friday: $97.30. You save $1.70, or 1.7%.
- "Compare at" or MRP prices. A list price or MRP may be higher than anyone actually charges. Compare with what the item sold for recently, not the printed maximum.
- Bundles. "Worth $300" may add up accessories you'd never buy separately.
How to check: look at the price on the same shop a few weeks earlier (screenshot items on your wishlist in early November), compare with two or three other shops, and if the site shows a price history, use it. Then run the calculator from the usual price, not the "was" price.
4. Decode the deal formats
| Deal | What it really is |
|---|---|
| Buy one, get one free | 50% off each, only if you wanted two |
| Buy one, get one 50% off | 25% off each (for two equal prices) |
| Spend $100, get $20 off | 20% off at exactly $100; less if you spend more |
| Free gift worth $50 | Worth $0 if you'd never buy it |
| 3 for the price of 2 | 33.3% off each, if you need three |
The test for every format: what would you have paid for what you actually wanted, and what are you paying now? Put both into the third line of the calculator.
5. Don't forget tax, shipping and currency
- Sales tax in the US is usually added at checkout on the discounted price. A $79.99 deal at 7.25% tax is $85.79. The sales tax guide shows the maths.
- Shipping can wipe out a small online discount. Add it before comparing with a shop that delivers free.
- Buying from abroad? Convert the price with the free currency converter and allow for card fees, import duty and longer returns.
6. Watch out for "no-cost" instalments
Sale checkouts push monthly instalments. Some "no-cost EMI" offers are genuinely interest-free; others build the interest into the price or add a processing fee. Work out the total you'll pay across all instalments and compare it with the one-time price. The no-cost EMI guide explains how these deals work.
A quick Black Friday deals checklist
- Write down the usual price of everything on your list now, before the sale.
- On the day, calculate the real % off from the usual price.
- For stacked offers, multiply the "pay" percentages.
- Add tax and shipping.
- Ask if you'd buy it at that price with no sale on.
Doing the sums in your head is quicker than you'd think; the percentage tricks post has shortcuts like "15% off = pay 85%". For more discount examples, see how to calculate a discount percentage.
Check a deal now
Type the usual price and the sale price into the third line of the free percentage calculator to see the real percentage off. It's free, needs no sign-up and works on your phone, so you can check a deal in the shop or in the checkout.
Frequently asked questions
- When is Black Friday in 2026?
- Friday 27 November 2026, the day after US Thanksgiving. Cyber Monday is 30 November.
- How do I calculate the percentage off a sale price?
- Subtract the sale price from the original, divide by the original and multiply by 100. $129.99 down to $89.99 is about 31% off.
- Is 30% off plus 15% off the same as 45% off?
- No. You pay 70% and then 85% of that, which is 59.5% of the price, so the total discount is 40.5%.
- How can I tell if a Black Friday deal is real?
- Compare the sale price with what the item usually sold for in recent weeks, at that shop and others, rather than the "was" or MRP price on the tag.
- Is "buy one get one 50% off" a good deal?
- It's 25% off each item when both cost the same, and only a saving if you wanted two.
Calculators
Try the Percentage Calculator
Free, no sign-up, works in your browser. Work out X% of a number, what percent one number is of another, and the percentage increase or decrease between two values, all on one page.