How much stock do you need for Black Friday?

Normal-week sales understate sale-week demand, and supplier lead times are longest in October and November. The useful question is: at sale-week pace, how many days does each best seller last, and is there still time for an order to arrive?

A quick manual version

1. Take last year's sale-week units per product, or your best week this year. With no history, assume 3 to 5 times your normal daily rate.
2. Add units on hand and units arriving before the sale. Divide by the sale-week daily rate to get days of cover.
3. Count back from the sale start by your real supplier lead time (use how long recent orders actually took, not the quote). That is your last order date.
4. If the date has passed, cap the promo on that product or take pre-orders instead of discounting it into a sell-out.

Or let the planner do it

Open the planner, upload your orders CSV, add a promotion with its dates and expected sales lift (try +100%, then +300%), and compare the order quantities and the chance of running out for each product. The lift is your estimate, so it works best for comparing scenarios. Everything runs in your browser.