How to spot stock-outs early with one spreadsheet

1. Days of stock left

Divide current stock by average daily sales. If you sold 70 units in the last 7 days and have 100 on hand, you sell 10 a day, so you have 10 days left.

2. Stock at arrival

If you order today, the goods arrive after the supplier's lead time. With a 5-day lead time you will sell another 50 before they land, so only 50 are left when the delivery comes in. If this number is close to zero, the order has to go out today, not next week.

3. How much to order

Pick how many days you want covered after the delivery arrives. We use 3 days as the minimum and 14 days as the comfortable amount. Then subtract what will still be on the shelf at arrival.

Mistakes that make the numbers lie

If a product was out of stock for a few days last week, its average looks lower than real demand. Divide only by the days it was actually in stock.

Take cancelled and returned orders out of the sales count.

Black Friday or a big promotion inflates the average. Leave promo days out, or plan them separately.

Doing this for hundreds of SKUs

By hand it takes too long, so we put it in a free calculator. Upload an Excel or CSV export with SKU, stock and recent sales, or just your raw order lines, and you get days left, run-out date and reorder quantity per SKU. It runs in your browser, so the file never leaves your computer.

Also useful: reorder point and safety stock calculator