Reorder point: definition, formula and how to set it for ecommerce

A reorder point answers one question per SKU: at what stock level do you place the next order so it lands before you run out?

What is the reorder point formula?

Oracle Inventory's reorder point planning documentation gives the textbook version:

Reorder point = forecast demand during lead time + safety stock

In that model, an order is due once on-hand stock plus planned receipts falls below that line. Shopify's retail guide writes it as daily sales velocity times lead time, plus safety stock. Each term needs an ecommerce-specific input:

Term	What it means	Where the number comes from
Daily demand	Forecast units sold per day	All channels, stockout days removed
Lead time	Days from placing the order to units being sellable	Order placement, production, freight, 3PL or AWD receiving, and FBA check-in
Safety stock	Buffer for demand and lead-time surprises	Forecast error and supplier delays, per SKU
Inventory position	What you compare against the reorder point	All locations, inbound shipments and open POs

Worked example: a SKU sells 25 units a day. Placing the order and production take 30 days, door-to-door ocean freight with port clearance 25, 3PL receiving 5, and the move into FBA through check-in 10. Lead time is 70 days, so lead-time demand is 1,750 units. With 250 units of safety stock, the reorder point is 2,000.

Safety stock has its own formulas. Oracle Inventory calculates it either as a percentage of forecast demand or as a service-level factor times 1.25 times the mean absolute deviation of forecast error. Lokad notes that normal-distribution methods fit poorly for SKUs with intermittent demand and for service levels above 90%.

Why does the reorder point matter for operations and growth?

It decides when cash turns into inventory. Too low and the order lands after the listing goes out of stock. Too high and cash sits in cartons, running up storage fees. Amazon's Restock Inventory help frames its own recommendations as that same trade-off: lost sales from running out against capital and storage costs from carrying too much.

It also decides when you need space. For professional accounts with 39 or more weeks in FBA, Amazon sets capacity limits monthly for each storage type, in cubic feet. Usage counts on-hand stock plus every open shipment from the day it is created, whether or not it has left. Overflow waits in AWD, a 3PL or your warehouse, and Amazon says AWD can auto-replenish FBA.

What mistakes make a reorder point wrong?

• Lead time counted as freight only. Oracle Inventory builds order lead time from preprocessing, processing and postprocessing; Amazon's Restock tool takes supplier lead time and your own lead time as separate settings. Skip a leg and every reorder point runs short.
• Checking FBA on-hand only. Compare against the full inventory position, or you double-order while a PO is on the water.
• Velocity taken from out-of-stock weeks. A SKU that was out for 10 of the last 30 days looks slower than it is, so its reorder point comes out too low.
• One flat buffer for every SKU. A steady seller and a seasonal item carry different risk.
• Set once, never updated. Amazon's Restock tool works from your sales history and demand forecast, and its units-shipped data refreshes daily. A number typed into a spreadsheet stays where you left it.

How does Growth OS set and act on reorder points?

The reorder point sits inside the replenishment gap, and a wrong one shows up as stockouts. Ecomsellertool Growth OS is deployed on your own accounts and is built to:

1. Track days of cover per SKU and channel.
2. Set reorder points from real lead times.
3. Draft purchase orders and shipment plans before a SKU runs out.
4. Keep stock in sync across your marketplaces, with 3PL, FBA and catalog counts reconciled daily.

Rules your operation needs beyond the base, such as a buyer approval step, capping FBA shipments at remaining capacity, or flagging SKUs where Amazon's Restock numbers disagree with yours, can be scoped and built as custom modules on top. You own the custom modules we build and your data; the Growth OS base is licensed to you.

Where should you start?

If best sellers keep running out while slow SKUs pile up, check the reorder math first. Start with the free Quick Scan in the Ops Gap Diagnostic: it works from uploaded reports, including an Inventory Ledger or Manage FBA Inventory report, and returns your top three operations gaps, each with a yearly dollar estimate. To see the base system first, look at Growth OS.