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Why a round number like 10 fails

One shared threshold of 10 across the whole catalog fails in two opposite directions at the same time.

• Fast sellers warn you far too late. Something selling 20 a day is gone within hours of passing 10. The email arrives after the moment you could have acted.
• Slow sellers warn you constantly. Something selling one a month sits under 10 all year and emails you every day about a situation that is perfectly fine.

The second one is what kills the whole system. When most alerts turn out to need no action, people learn to ignore all of them, including the one that mattered. Alerts everybody filters away are worse than no alerts, because you still think you are covered.

How to work out your threshold

Step 1: units sold per day

Take the units you sold over a recent stretch and divide by the number of days in it. Ninety days usually works well. It is long enough to smooth out odd weeks and short enough to reflect what is selling now. Use a shorter stretch for anything moving fast right now.

Step 2: days to restock

The real number of days from spotting the problem to having stock you can sell. Not the number your supplier quotes. It includes your own sign off, their production, shipping, customs if you import and the time it takes to book the delivery in. This is the number almost everyone gets wrong.

Step 3: a safety buffer

Cover for the weeks you sell more than usual or your supplier runs late. A quarter to a half of the units you sell during a restock is a good starting point, more for anything unpredictable. The full version is in the safety stock formula.

Two worked examples with real numbers

A fast selling basic

• Sells 12 a day
• Restocks in 14 days
• Units sold while you wait: 12 × 14 = 168
• Buffer at a third: 56
• Threshold: about 224

Set this product to 10 and you would be placing the order with about twenty hours of stock left, against a two week wait. It would sit empty for nearly two weeks.

A slow selling accessory

• Sells 0.2 a day, about six a month
• Restocks in 10 days
• Units sold while you wait: 2
• Buffer: 2
• Threshold: about 4

Set this one to 10 and it emails you all year about a product that is never actually at risk.

The shortcut for a big catalog

Doing this properly for a thousand SKUs by hand is not realistic. It is also not necessary. Here is the version that works.

1. Do the sum properly for your top 20 products by revenue. That is where most of the money is.
2. Put the rest into three or four groups by roughly how fast they sell and how long they take to restock. Give each group one sensible number.
3. Fix single products when an alert turns out wrong. An alert that came too late means raise the number. One that has been pointless for a month means lower it.

You end up with a good setup within a couple of months, for a fraction of the work.

How often to review your thresholds

Thresholds go stale because the numbers behind them move. Sales rise and fall with the seasons, suppliers get slower or faster and products swap between fast and slow sellers.

Once a quarter over your top sellers is enough for most stores, plus a look before any busy period. Raise the numbers before a peak rather than during it, because that is exactly when suppliers get slower at the same moment sales speed up.

Thresholds that live on the product

Stockwell keeps a separate number for every SKU, so a fast seller can warn you at 224 while an accessory warns at 4. Both stay worth reading and neither turns into noise.

Get it on the Shopify App Store Free plan covers 50 SKUs with a daily summary. Paid plans add instant alerts and more recipients. No card needed to start.