Reorder Point: What It Is and How to Calculate It

There's a moment in every stock cycle where you should stop and reorder. Wait too long and you run out before the next shipment lands. Jump too early and you pile up stock you didn't need yet. The reorder point is the number that catches that moment for you, automatically, so it doesn't depend on someone noticing a shelf looking thin.

It's one of the most useful calculations in inventory management and one of the easiest to get slightly wrong. Here's the formula, a worked example with real numbers, and how it connects to safety stock.

What a reorder point is

The reorder point is the inventory level that triggers a new purchase order. When stock for a SKU drops to that level, you order more, timed so the new shipment arrives just as you're about to run out.

It answers a specific question: given how fast this item sells and how long my supplier takes, at what stock level do I need to act so I don't stock out while I wait? Set it correctly per SKU and reordering stops being a judgment call and becomes a signal.

The reorder point formula

The formula has two parts:

The first part, demand × lead time, covers the stock you'll sell while you wait for the order to arrive. The safety stock sits on top to absorb the days that run hotter than average and the shipments that run later than promised.

A worked example

Say you sell a SKU at an average of 25 units a day. Your supplier's lead time is 8 days. You've calculated a safety stock of 60 units for this item.

• Demand during lead time: 25 × 8 = 200 units
• Plus safety stock: 200 + 60 = 260 units

Your reorder point is 260. When on-hand for that SKU hits 260, you place the order. In a normal stretch, you'll sell roughly 200 units over the 8 days it takes the shipment to arrive, landing near your 60-unit buffer right as the new stock comes in. If demand spikes or the shipment slips a couple of days, the buffer covers you.

Change any input and the trigger moves. A longer lead time pushes the reorder point up. A faster-selling item pushes it up. That's the point. The number reflects the actual behavior of that specific SKU.

Reorder point vs. safety stock

These two get tangled together constantly, so it's worth being precise.

• Safety stock is a cushion. It's the buffer you aim never to dip into, sitting there as insurance against the unexpected.
• Reorder point is an action signal. It's the level that tells you to do something (place an order), and it includes safety stock plus the demand you expect during the lead time.

One is a quantity you hold. The other is a trigger that fires. Safety stock is an ingredient inside the reorder point, not a separate alarm. If you've already calculated safety stock per SKU, you're most of the way to your reorder points.

Why one blanket number fails

The temptation is to set a single reorder point ("reorder anything under 100") and move on. It doesn't work, because demand and lead time vary wildly across a catalog.

Consider two SKUs:

• A fast mover selling 40 a day with a 14-day lead time. Its demand during lead time alone is 560 units. A blanket reorder point of 100 means you'd stock out roughly two weeks before the new shipment ever arrives.
• A slow mover selling 2 a day with a 3-day lead time. Its demand during lead time is 6 units. A reorder point of 100 means you're carrying weeks of dead stock and reordering far too early.

Same trigger, two opposite failures. Reorder points have to be per SKU because the inputs are per SKU. There's no shortcut around that.

Keeping reorder points accurate

A reorder point is only as good as the inputs behind it, and those inputs drift:

• Demand changes. Seasonal swings, a product gaining traction, a line fading out. Recalculate when sales patterns shift.
• Lead times change. A new supplier, a port delay, a freight change. A reorder point built on a 7-day lead time is dangerous if your supplier now takes 12.
• Safety stock changes. Since it feeds the reorder point, any change to your buffer changes the trigger.

This is exactly the kind of bookkeeping that's tedious by hand and well suited to software. A system that knows each SKU's demand and lead time can recalculate reorder points continuously and flag items the moment they cross the line, so reordering becomes something the system watches rather than something you hope someone catches in time.

Set your reorder points per SKU, build them on real demand and lead-time data, and revisit them when the inputs move. Done right, you stop firefighting stockouts and stop drowning in early reorders, and the shelf stays full without anyone staring at it.