Shopify low stock alert: why it fires too late, and how to fix it

A low stock alert is supposed to tell you to reorder before you run out. For a Shopify store whose suppliers deliver in days, a simple alert at a fixed number of units works well enough. For a store whose suppliers take three or four weeks, it often arrives after the point where reordering could have prevented the stockout.

This guide explains why that happens, the common ways to set up an alert in Shopify, and how to choose a threshold that actually arrives in time.

Why a fixed threshold fires too late

A threshold such as "alert me when stock drops below 50" makes one silent assumption: that 50 units is enough to last until a new order arrives. Whether it is depends on two things that change:

• How fast the product sells. At 2 a day, 50 units last 25 days. At 10 a day, they last 5.
• How long the supplier takes. If the next delivery is 28 days away, 50 units at 5 a day runs out 18 days before it arrives.

So the same threshold can be comfortable for one product and far too late for another, and a threshold that was right in spring can be wrong by the holidays. The alert is not broken. It is answering "is stock low?" when the question that matters is "will stock last until the next delivery?"

The threshold that arrives in time

The level you want to be warned at is the reorder point:

Alert level = daily sales × (lead time + safety days)

For a product selling 5 a day from a supplier with a 28-day lead time, with 7 safety days:

5 × (28 + 7) = 175 units

That is more than three times the "50 units" that felt sensible. Our reorder point calculator guide has the full calculation, including stock already on order, and spreadsheet formulas.

Set it in days, not units

The cleanest fix is to stop thinking in units at all. Track days of stock left:

Days left = (available + on order) ÷ daily sales

Then alert when days left falls below the supplier's lead time plus a safety margin. A product that suddenly sells faster drops below that line sooner, without anyone changing a threshold.

Ways to get a low stock alert in Shopify

There are three common routes. Check Shopify's documentation and your plan for what is available to you, since features and plans change.

1. Check the Inventory page by hand

The Inventory page in the Shopify admin lists available stock per product and location, and you can sort by quantity. It costs nothing and works for a small catalog if someone looks at it on a fixed day every week. It does not tell you anything about sales pace or lead time.

2. Shopify Flow

Shopify Flow can start a workflow when stock changes. Its trigger is called Product variant inventory quantity changed, and it fires when a variant's inventory changes from an order, a manual adjustment or an app. A typical workflow:

1. Trigger: product variant inventory quantity changed.
2. Condition: the new quantity is at or below your threshold, and the previous quantity was above it, so you get one alert per crossing rather than one per sale.
3. Action: send an internal email or a message to your team.

Flow gives you control over who is told and when. The threshold is still a number you choose, so the work of setting it per product from sales pace and lead time, and updating it as both change, is still yours.

3. A low stock or inventory planning app

The Shopify App Store has apps that range from simple threshold alerts to full forecasting. When you compare them, ask:

• Does it set the alert from sales pace, or do I type a number per product?
• Does it know each supplier's lead time?
• Does it count stock already on order, so I am not told to reorder something that is on its way?
• Does it tell me how many to order, or only that I am low?
• Does it handle packaging and other supplies that are used per order rather than sold?

Stock on order: the other half of a useful alert

An alert that ignores stock on order keeps firing after you have reordered. Teams learn to ignore it, and then miss the one that matters. Any alert, manual or automatic, should compare the threshold against available stock plus units on confirmed purchase orders that have not arrived.

In Shopify, the inventory export includes an Incoming column for stock on its way that you have recorded in Shopify. If you track supplier orders somewhere else, such as a spreadsheet or email, you will need to add those units yourself.

A five-minute weekly check

If you are not ready to automate, this catches most problems:

1. Export inventory and the last four weeks of orders.
2. For each product, divide units sold by 28 to get daily sales.
3. Divide available plus incoming by daily sales to get days left.
4. Sort by days left, smallest first.
5. Anything with fewer days left than its supplier's lead time plus a week needs ordering today.

Watch for products that were out of stock during the four weeks. Their sales look lower than real demand, so they will look safer than they are.

Where Reorder Day fits

Reorder Day replaces the threshold with the calculation above. For Shopify stores, you upload two admin exports each week (inventory and orders, about two minutes). It works out each product's sales pace, compares days of stock left with the lead time you set for its supplier, counts Shopify's Incoming or the purchase orders you mark sent, and emails you a draft purchase order per supplier for what needs ordering now. If your exports are more than six days old, it emails you a reminder to upload fresh ones instead.