Shopify's Days of Inventory Remaining: What It Tells You and When It's Wrong

How Shopify calculates it

Shopify’s inventory report help (opens in a new tab) defines both numbers:

• Days of inventory remaining is the stock you have left divided by the average units sold per day. The average comes from the variant’s sales over the last 28 days. A variant with no sales shows N/A, and one with negative stock shows 0.
• Sell-through rate is units sold divided by units sold plus units left, over the most recent 30 days. Sell 30 and have 70 left, and the rate is 30 out of 100.

Shopify notes that the sell-through data runs about two days behind, closer to three in time zones far ahead of UTC, so the latest busy days aren’t in it yet. Shopify’s Products page help (opens in a new tab) explains the bar itself, and each number links to its full report.

1. Sold-out days make best sellers look slow

The average is units sold divided by days, and Shopify’s help doesn’t say it leaves out the days a variant was sold out. A stretch with nothing to sell counts as days with no sales.

This hits the products that matter most. The best seller that keeps selling out looks like an average product, so you order too little and it sells out again. For those, divide the units sold by the days it was actually in stock.

2. It doesn’t know how long your supplier takes

Twenty days of stock sounds comfortable. If your supplier takes 21 days to deliver, you’re already late. The number only means something next to the lead time: order when days remaining is close to the supplier’s delivery time plus the days until you next place an order. The same arithmetic works for a low stock alert.

3. It doesn’t count stock on its way

Days remaining divides the stock you have now. A purchase order that lands next week isn’t in it, so a product you’ve already reordered still looks urgent. Check your open purchase orders before you order the same thing twice. Our guide to Shopify purchase orders covers where to find them.

How to use it anyway

• Treat the lowest numbers as a shortlist to check, not an order list.
• For any product that sold out in the last month, work out the rate over the days it was in stock.
• Compare each number with that supplier’s delivery time, not with a gut feel.
• Take off what’s already on order.

Our reorder guide turns those steps into a quantity for each product.

A sales rate that knows when you were sold out

Efficiencia’s Reorder list makes those corrections for every product. From the day you install it, it records each product’s stock once a day. When it works out a sales rate from the last 60 days, it leaves out the days the product was sold out. It compares the stock with the supplier’s lead time, and counts the stock already on order.

Every line explains its number in a sentence, for example: “You sold 42 in 45 days in stock (sold out for 15 of the last 60), 0.93 a day.” The rest of the sentence names the lead time, the stock you keep and what to order.

Efficiencia is still in development. If you’d like to try it on your store, join early access.