When should you reorder inventory?

The basic rule

Days of stock left is units on hand, plus units on the way, divided by expected daily sales. Lead time is the days from placing the order to having stock ready to ship, including production, freight and receiving.

When days of stock left falls to lead time plus your safety days, place the order. Not when the shelf looks low.

Why last month's sales are not enough

Many brands reorder from past sales plus a fixed buffer. Then marketing runs a campaign nobody told operations about, and the best seller sells out in days. Meanwhile a product ordered months ago on old numbers sits on the shelf.

The forecast has to include what marketing has planned: ad spend, launches, email offers and influencer posts. Seasonality matters too.

Run it as scenarios

Here is an example. At the current sales rate, a product runs out in 47 days. With the planned campaign it runs out in 23. With aggressive scaling, 15. The supplier needs 35 days. The first case is fine. The other two are a decision: expedite an order now, or cap spend on that product.

Seeing all three side by side turns a surprise stockout into a choice made in advance.

When stock is short anyway

If a product will run out before new stock lands, slow it down on purpose. Cut ad spend on it, move creative to a product with plenty of stock and a good margin, and remove discounts so the remaining units last longer.

Who owns it

Operations owns the numbers. Marketing shares its plan before the campaign, not after. Review days of stock for your top products every week, in the same meeting where spend is decided. Check minimum order quantities and lead times with your suppliers every quarter.