When to reorder FBA inventory: a practical worked example

An FBA reorder decision starts with a date: when will the next batch actually be available to sell? Counting the units on hand is useful, but the same stock balance can be comfortable for a product replenished in a week and urgent for one replenished in a month.

Amazon’s inventory guide describes a reorder point using average daily sales, lead time, and buffer stock. This article applies that familiar approach to a hypothetical FBA workflow. The numbers below are examples, not Amazon requirements, a fee calculation, or a forecast for your store.

Define the clock you are trying to cover

For planning purposes, measure from the day you commit to a replenishment order to the day its stock becomes sellable. Break that elapsed time into stages you can observe: supplier preparation, transit to your prep location, preparation, outbound transit, and the remaining wait before inventory is available.

Use your own recent shipment records. Do not count overlapping stages twice, and do not assume that a carrier delivery scan means every unit is immediately sellable. Record both dates so the planning model reflects the experience of your products.

Work through one SKU

Suppose a hypothetical product has the following planning assumptions:

• Average demand: 8 units per day.
• Elapsed replenishment time: 24 days from ordering to sellable stock.
• Extra buffer: 7 days of demand.
• No outstanding replenishment orders or unfilled customer commitments.

Demand during replenishment is 8 × 24 = 192 units. The buffer is 8 × 7 = 56 units. Together, those assumptions produce a reorder point of 248 units.

In this deliberately simple case, reaching 248 sellable units is the signal to place the next order. It is not the order quantity. Deciding how much to buy also requires a target coverage period, cash budget, supplier minimums, and an assessment of how long the product may sit.

Account for orders already in motion

Now change the example. You have 160 sellable units and a confirmed 120-unit replenishment expected to become available in ten days. At eight units per day, the existing stock covers twenty days. If that arrival date holds, the shipment can replenish stock before the original balance runs out.

But moving the same arrival to day twenty-five changes the answer: a total of 280 units across locations does not prevent a gap around day twenty. This is why adding every inbound unit to a single stock total can hide a timing problem.

Keep a simple dated schedule of expected receipts and demand. Distinguish confirmed orders from proposed purchases, and record each receipt once. Use the reorder point as a prompt to review that schedule, not as an instruction to duplicate an order already placed.

Check whether the sales average is believable

Eight units per day is only useful if it represents the demand you expect to serve. Review periods with stockouts, temporary promotions, price changes, and unusual large orders before choosing a planning rate.

Test a second scenario. At ten units per day, the same 31-day lead-time-plus-buffer assumption calls for 310 units, a difference of 62. That comparison exposes how sensitive the decision is to demand without pretending the higher number is certain.

Make the weekly review actionable

For each priority SKU, record the sellable balance, recent demand, next confirmed receipt date, supplier lead time, and the person responsible for the next action. Note what changed since the last review.

Separate the outcomes into three actions: place a new order, follow up on an existing shipment, or hold because coverage is adequate. A low balance with a dependable incoming receipt needs a different response from a low balance with no purchase order.

If multiple channels consume the same inventory pool, include their demand in the same review. Our guide to Amazon’s multichannel rollout covers the mapping and reconciliation checks to make before connecting more channels.

The goal is a repeatable decision that someone else on your team can audit: the demand assumption, the expected arrival, the buffer, and the action are all visible in one place.