Guides  /  How Forecasting Works

Guide ยท 4 min read

“Stockout in 10 days” Isn’t Enough. Here’s What You Actually Need to Know.

Say you’ve got 100 units left. You’re selling about 10 a day. Simple math says you’ll run out in 10 days.

So your inventory tool tells you: “Stockout in 10 days.”

Okay. Now what?

That number feels useful, but it doesn’t actually tell you what to do. It tells you when the shelf goes empty — not when you need to act.

The missing piece: your supplier isn’t instant

Here’s the part most stockout warnings skip: your supplier takes time.

If your lead time is 5 days, and you wait until day 10 to place an order, you’re already too late. The stock runs out 5 days before your new order even arrives.

The number that actually matters isn’t “when will I run out.” It’s:

“When do I need to order, so I don’t run out.”

Same example, now with lead time factored in:

  • 100 units left
  • Selling ~10/day → stockout in 10 days
  • Supplier needs 5 days
  • Order by day 5, not day 10

That’s the difference between a warning and an instruction. One makes you think. The other tells you what to do.

Same math, two dates: the stock runs out at day 10 — but the order has to go out by day 5. The gap in between is your supplier’s lead time.

Don’t fake precision you don’t have

Here’s where a lot of inventory tools quietly get it wrong: they assume a lead time (often just a default, like “7 days for everyone”) and show you a clean, confident date anyway.

“Order by Sep 21” looks precise. It looks like the tool knows something. But if that 7-day number was never actually measured — just a guess baked into the settings — the date is a guess wearing a confident outfit.

That’s worse than no date at all, because it looks trustworthy when it isn’t.

The honest version looks more like this:

  • If you don’t have real delivery history for a supplier yet: “Order-by date unavailable — not enough lead time data yet.”
  • Once you do have real data: “Typical lead time: 6 days, based on your last 8 deliveries → Order by Sep 22.”

One is guessed. The other is earned. They should not look the same on screen.

What this looks like in practice

One line at the bottom tells you exactly what to do. No extra math required.
When there isn’t enough delivery history yet, it says so — instead of showing a date that was never really calculated.

The takeaway

A stockout date tells you about a problem. An order-by date tells you what to do about it.

If your inventory tool only gives you the first one, you’re doing the second calculation yourself — in your head, probably while also doing five other things.

Related guides

Why Your Reorder Number Might Be Too High (And It’s Not Your Fault) Why We Sometimes Say “Rough Estimate” Instead of a Clean Number

We build Invocast, an inventory forecasting app for Shopify stores. This “order-by date, not just a stockout warning” idea is one of the things it’s built around.

Never calculate an order-by date by hand again.

Invocast tracks your sales pace and supplier lead times — and tells you exactly when to order.

Try Invocast Free for 14 Days

14-day free trial · No credit card required