A stock count tells you how many units you have. It doesn't tell you how long they will last. Days of inventory remaining turns a quantity into a deadline, and this guide shows how to calculate it and what to compare it against.
The formula
Divide the units you have on hand by the average number of units you sell per day. The result is roughly how many days of selling you have left at the current pace.
- Units on hand: What you can sell today
- Average daily sales: Units sold in a period, divided by the days in that period
- Days remaining: Units on hand ÷ average daily sales
Work it through
Say you have 180 units of a product, and you sold 84 units over the last 28 days. That's an average of 3 a day, so you have about 60 days of stock left.
| Input | Value |
|---|---|
| Units on hand | 180 |
| Sold in the last 28 days | 84 |
| Average daily sales | 3 |
| Days of inventory remaining | 60 |
Where to find it in Shopify
Shopify calculates this for you in the Inventory remaining per product report. In your admin, go to Analytics, then Reports, and filter the category to Inventory. The report divides each variant's ending quantity by its average daily sales, using the last 28 days as the sales window.
- No sales in the period: The variant shows N/A instead of a number
- Negative ending quantity: The variant shows 0
- Related report: Inventory sold daily by product shows the average units sold per day for each variant
Compare it to your lead time
The number only means something next to your supplier's lead time. If a product has 20 days of stock left and your supplier takes 30 days to deliver, you are already late, even though the shelf looks full.
- ✅ Days remaining well above lead time: no action yet
- ❌ Days remaining close to lead time: order now
- ❌ Days remaining below lead time: expect a stockout, and consider a faster shipping option
To turn this into a trigger you can act on, set a reorder point with a safety stock buffer.
Where the simple version goes wrong
A straight average assumes the next month looks like the last one. That breaks down in a few common situations, so treat the number as an estimate, not a promise.
- Trend: A product growing week over week will run out sooner than the average suggests
- Seasonality: A 28-day window in a slow month understates demand in a peak month
- Stockouts: Days with zero stock have zero sales, which drags the average down and makes the product look slower than it is
- Promotions: A sale week inflates the average and makes stock look shorter than it is
Doing this at scale
StockSense forecasts demand for each SKU from your order history, using velocity, trend, seasonality and lead-time-aware safety stock. It recommends a reorder point, quantity and date, ranks SKUs by revenue at risk, and drafts purchase orders grouped by supplier. See StockSense.