Days of inventory on hand (DOH) tells you how many days your current stock will last at your normal sales rate. It turns an abstract stock count into a countdown — "18 days of stock left" is far more useful than "142 units".
The DOH formula
Two ways to get there — one at the business level, one per product.
DOH = (Average inventory ÷ COGS) × 365
Or, per product, the version you'll use day to day:
Days of stock = Units on hand ÷ Sales per day
Worked example
A product with 90 units on hand selling 5/day has 90 ÷ 5 = 18 days of stock. If the supplier's lead time is 14 days, you're cutting it close — time to reorder.
DOH, turnover and reorder point
- Turnover — DOH is just the flip side of the inventory turnover ratio:
DOH = 365 ÷ turnover. A turnover of 6 ≈ 61 days on hand. - Reorder point — compare DOH to your supplier lead time. When days of stock ≈ lead time + a buffer, you've hit your reorder point.
- Sales velocity — DOH is only as good as your sales-per-day figure, so use a recent window.
Reading the number
- Very low DOH — you're about to stock out; reorder now.
- Very high DOH — overstock; cash tied up in slow-moving product.
- Healthy DOH — comfortably above lead time, without months of dead stock.
See it for every product
Foreshelf shows days of stock left for every product from your Shopify sales history and flags the ones running low or sitting overstocked — so you act before it's a problem. See the full method in how to forecast inventory on Shopify.