Most BFCM margin damage is decided in October, when someone picks a headline discount without
Black Friday 2026 falls on 27 November and Cyber Week runs 27 November to 3 December, so offer structure needs to be settled by late October.
A flat sitewide percentage is the easiest offer to build and the hardest to recover from, because it discounts your best sellers at the same rate as your slowest stock.
Threshold and bundle mechanics raise average order value instead of cutting unit margin, which is why they survive contact with a spreadsheet.
Model the discount against contribution margin, not gross margin — shipping, payment fees and BFCM return rates all move against you at once.
Black Friday falls on Friday 27 November 2026 and Cyber Monday on Monday 30 November, with Cyber Week generally treated as 27 November to 3 December.
The full guide has the formats, the deadlines and the worked examples.