Every year the same question comes up: should you buy now in the Black Friday sales, or wait for the January sales? There is no rule that one is always cheaper. Some products hit their lowest price in late November, others in January when shops clear winter stock. What you can do is compare the two deals properly — and that comes down to a little discount maths.
Compare final prices, not percentages
A bigger percentage does not mean a lower price. The percentage is always taken from a reference price, and that reference can change between sales.
Example: a coat is £200 in November.
- Black Friday: 30% off → £200 × 0.70 = £140
- January: 40% off → £200 × 0.60 = £120
January wins by £20 here. But if the shop raised the "regular" price to £230 in December, 40% off gives £138 — almost the same as Black Friday. Always write down the final price you pay, then compare those.
Stacked discounts don't simply add up
January sales often advertise "extra 20% off sale prices". Two discounts in a row are multiplied, not added:
- 25% off, then an extra 20% off: 0.75 × 0.80 = 0.60 → 40% off in total, not 45%.
- 20% off, then an extra 10% off: 0.80 × 0.90 = 0.72 → 28% off, not 30%.
- 50% off, then an extra 20% off: 0.50 × 0.80 = 0.40 → 60% off, not 70%.
So a £200 item at "25% off + extra 20%" costs £120 — the same as a straight 40% off. The Discount Calculator has an optional "extra discount" field for exactly this case.
Check the "was" price
A discount is only as honest as the price it starts from. If a TV is "£250, now £150", that looks like 40% off. If it actually sold for £180 most of the autumn, the real saving is (180 − 150) ÷ 180 = 16.7%.
To see the real discount, enter the price you have actually seen it sell for and the sale price into the calculator's "discount % from two prices" mode. You can also work backwards from a sale price: £84 after "30% off" means the original was £84 ÷ 0.70 = £120 (here is how).
Track the price yourself
You don't need special software. A note on your phone works:
- Pick the few items you really want before the sales start.
- Write down the date, shop and final price each time you check (including delivery).
- When a new deal appears, compare it with the lowest price in your notes, not with the shop's "was" price.
- Use the Percentage Decrease Calculator to see how much cheaper a new price is. A drop from £140 to £126 is 10%; from £140 to £120 it is 14.3%.
So which sale should you wait for?
- Buy at Black Friday if the item is a gift for December, or the November price is already the lowest you have recorded.
- Wait for January for seasonal stock (winter clothes, decorations) that shops want to clear, and if you can live without it for a few weeks.
- Skip both if the "deal" is only a percentage off a price you never saw it sell for.
Remember returns too: a slightly higher price with a long returns window can be the better buy.
FAQ
Are January sales cheaper than Black Friday? Sometimes. It depends on the product and the shop. Compare the final prices you have recorded, not the advertised percentages.
How do I calculate two discounts together? Multiply what is left after each one: 30% then 15% off is 0.70 × 0.85 = 0.595, so you pay 59.5% — a total of 40.5% off.
Is "up to 70% off" a 70% discount? Only on a few items at most. Check the price of the item you want.
Try it now
Work out any deal with the free Discount Calculator, including stacked "extra % off" offers — it runs entirely in your browser.