Amazon Inventory Management: A Seller's Guide

Most ecommerce leads who come to me start the same way: "We sell on Amazon and eBay, our listings are a mess, and we keep running out of our best products." Here is how inventory actually works on Amazon, where it falls apart as you scale, and the honest call on when to hand the daily work to a dedicated team.

How Amazon inventory management works

Set reorder points and forecast demand

A reorder point is the stock level that triggers a new purchase order, calculated from your daily sell rate times your supplier lead time, plus a safety buffer. Get it right and you never stock out on a bestseller. Get it wrong and you either lose the Buy Box to a stockout or you bury cash in dead stock. Forecasting layers on top: account for seasonality, your Q4 surge, and supplier delays before they hit.

Keep a 30 to 60 day supply

The working target most sellers land on is 30 to 60 days of stock. Less than that and one shipping delay puts you out of stock. More than that and you start paying to store units that are not moving. The balance is the whole game, and it shifts SKU by SKU.

Watch your FBA stock health

Amazon gives you built-in dashboards for this. The Manage Inventory and FBA Inventory consoles show inbound units, reserved units, and anything flagged as stranded, unfulfillable, aged, or excess. Stranded inventory is stock Amazon is holding that has no active listing attached, so it sits there earning fees and selling nothing. Checking these dashboards is a daily job, not a monthly one.

Sync inventory across channels

If you sell across Amazon plus Shopify and marketplaces like eBay and Walmart, every sale on one channel has to decrement the count on all of them. Miss that sync and you oversell, cancel orders, and tank your seller metrics. This is where a multi-channel listing tool plus a person watching it earns its place.

The IPI score and aged inventory

Two numbers decide whether Amazon penalizes you. The first is the Inventory Performance Index (IPI), a score from 0 to 1000 that measures how efficiently you manage FBA stock. Keep it above 350 to 400 and you stay clear of storage limits and overage fees. A score from 400 to 800 is the healthy range. It is driven by excess inventory, your sell-through rate, stranded units, and in-stock rate.

The second is aged inventory. Amazon charges aged-inventory surcharges on units stored past 271 days, and the penalty escalates hard once units pass 365 days. The fix is to catch slow movers early: run a promotion, add sponsored ads to lift sell-through, or file a removal order before the surcharge stacks up. Your sell-through rate, sales over the last 90 days divided by average available inventory, is the early warning that tells you which SKUs are heading for that surcharge.

Where it breaks at scale

The math is the same whether you run 20 SKUs or 2,000. What changes is the load. At volume, three things fail first. Reorder points stop getting checked daily, so bestsellers stock out and slow movers pile up. Aged inventory surcharges sneak in because nobody is watching the 271-day clock across hundreds of units. And multi-channel sync drifts, so you oversell and eat cancellations. None of that is a strategy problem. It is a capacity problem. Someone has to do the boring, repeatable work every day, and a founder running the business does not have those hours.

When to outsource Amazon inventory management

Here is the honest trade-off. In-house, you get full control and instant context, but you are either doing it yourself at the cost of growth work, or hiring a US ecommerce coordinator at $50,000 to $60,000 a year loaded, which is heavy for a task that is mostly daily monitoring. Outsourcing gives you a dedicated, pre-trained assistant who runs the daily execution inside your existing tools, at $7 an hour with no setup fee. You keep the buying and pricing decisions. They handle the volume.

Outsource when stockouts and aged-inventory fees are costing you more than a dedicated person would, when multi-channel sync is eating your week, or when inventory work is pulling you off product and marketing. A trained ecommerce operations team handles reorder-point monitoring, FBA replenishment, removal orders, stranded-inventory cleanup, and listing and inventory sync that keeps Amazon aligned with Shopify and your other marketplaces like eBay and Walmart, under US management and ISO 27001 security. Many sellers staff this through an ecommerce virtual assistant who owns the daily checks so you do not have to. National Workwear runs thousands of Shopify SKUs with our team, and Elite Commerce Group put us through a 50,000-SKU catalog migration on a 60-day deadline at 99.8% accuracy. It is the same pattern across every operations engagement: keep the judgment in-house, outsource the daily labor.

FAQs

What is Amazon's inventory management system?

The process of tracking and controlling stock in Amazon's network so you meet demand without stockouts or excess storage fees. Sellers run it through native FBA dashboards plus reorder points, sell-through tracking, and multi-channel sync.

What are the 4 types of inventory management?

Raw materials, work-in-progress, finished goods, and MRO supplies. For an Amazon seller, finished goods is the one that matters: the sellable units in FBA centers or your warehouse waiting to ship.

What is a good IPI score on Amazon?

IPI runs from 0 to 1000. Keep it above 350 to 400 to avoid storage limits and overage fees. A score from 400 to 800 is healthy.

How much does Amazon take from a $100 sale?

A referral fee (commonly 15% by category) plus an FBA fulfillment fee by size and weight, plus storage fees. A working number for many sellers is 30% to 40% of the sale across all Amazon fees, which is why avoiding storage penalties protects your margin.

Stocking out on bestsellers while slow movers rack up storage fees? Get a custom quote. Dedicated ecommerce teams deploy in 7 days, US-managed, ISO 27001 certified.