Short version: Amazon inventory management comes down to three numbers per SKU: sales velocity, supplier lead time and days of cover. Reorder when available plus inbound stock falls to velocity x (lead time + safety days). Stockouts cost sales. Overstock costs cash and fees. Check both every week.

A stockout is a lost sale today and a weaker listing tomorrow. Overstock is cash sitting in a warehouse while storage and aged-inventory charges accrue. Most reorder mistakes come from one wrong input: a lead time that leaves out check-in, or a sales rate taken from the wrong window.

OptimalCentral is the operating system for your Amazon business. On the free and Pro layers the agent audits your stock and you act on it. On a connected Brand account it also scans your FBA inventory every day and emails you when a SKU crosses into a risk state. It never places an order. Ordering spends your money, so that stays your decision.

The five numbers that run inventory

  • Sales velocity: average units sold per day. Use a recent window, such as the last 28 days, and note any promotion inside it.
  • Lead time: days from placing the purchase order to units being sellable on Amazon. Count production, freight to the warehouse and Amazon check-in. Check-in is the step most people leave out.
  • Safety stock: extra days of cover that absorb delays and demand spikes. 14 days is a common starting point. Use more for launches or unreliable suppliers.
  • Reorder point: the stock level that triggers an order.
  • Days of cover: how long current stock lasts at the current sales rate.

Count inbound units (shipped, not yet received) together with available units. Inbound stock only helps once it is sellable, so keep an eye on the gap between shipped and received.

The reorder math, step by step

  1. Days of cover = (available + inbound units) / daily velocity.
  2. Reorder point = daily velocity x (lead time + safety days).
  3. Reorder when available plus inbound units is at or below the reorder point.
  4. Order quantity = daily velocity x target days of cover on arrival, minus units you expect to still have on arrival (current position minus velocity x lead time).
Example — illustrative numbers

Velocity: 280 units over the last 28 days = 10 a day.

Lead time: 35 days. Safety: 14 days.

Reorder point: 10 x (35 + 14) = 490 units.

Position today: 400 available + 120 inbound = 520 units, so 52 days of cover. That is above 490, so not yet. In 3 days it hits 490. Order then.

Order size: you want 60 days of cover on arrival. Using today's 520 as the position: units left on arrival = 520 - (10 x 35) = 170. Needed = 10 x 60 = 600. Order 430, then round up to your supplier's minimum order and case pack.

The formula assumes steady demand. Seasonal peaks, launches and price cuts change velocity. Rerun the numbers whenever velocity moves noticeably, and use a forecast window that matches the season you are ordering for.

Stockout risk: what a gap costs

While a SKU is out of stock you lose its sales outright. You also lose your place on shared listings: an offer you cannot ship cannot hold the Buy Box. Ads keep spending on a listing that cannot convert, which pushes ACOS up for the days it takes to restock. Plan the reorder so units are sellable before cover reaches zero, not merely shipped.

If stock goes missing inside Amazon's network rather than selling through, that is a different problem. Units Amazon loses or damages can be claimed back. See the FBA reimbursement guide.

Overstock risk: what extra cover costs

Cash tied up in slow stock cannot fund the next order. Amazon also charges for storage and for units that sit past its inventory-age thresholds. The fee schedule changes, so read the current one in Seller Central instead of relying on a number from a blog. A practical rule: flag any SKU whose days of cover is far above lead time plus your target, and check inventory age before the next surcharge date.

Options for overstock: slow or pause inbound shipments, run a price promotion, or remove units. Pick by margin, not by habit. Per-SKU profit shows which SKUs can afford a discount.

A weekly checklist

  • ☐ Velocity refreshed from the last 28 days, promotions noted
  • ☐ Lead time per supplier confirmed, including check-in
  • ☐ Every SKU's days of cover compared with its lead time
  • ☐ SKUs at or below reorder point listed, with order quantity
  • ☐ Shipped versus received gaps on inbound shipments checked
  • ☐ SKUs with cover far above target flagged for slowing or clearing
  • ☐ Inventory age checked for units approaching a surcharge tier
  • ☐ Listings behind a stockout checked for ads still spending

Stock is one input to a healthy listing. For the rest, run through the listing audit checklist.

Doing it without a spreadsheet

The OptimalCentral Inventory Planner reads your FBA inventory report through your seller connection. It computes days of cover from sales velocity against available plus inbound stock, marks each SKU reorder now, reorder soon, ok or overstock, and suggests an order quantity that covers your lead time plus target cover. You set the supplier lead time and cover target. It also shows aged units and Amazon's own estimates of storage and surcharge cost. It is included on every plan.

On a Brand account (and during the 14-day trial) the agent scans your inventory daily and emails you on the day a SKU enters trouble. It alerts on changes, not states: an overstocked SKU you already know about stays on the page. Alerts are read-only. Purchase orders are drafts you review and place yourself.

Vendor Central accounts: the Vendor Inventory tool on the Enterprise plan reads your vendor inventory report per ASIN, with weeks of cover next to Amazon's lead time. It is a separate tool for a separate account type.

See which SKUs run out before your next shipment lands

Connect your seller account and get days of cover, reorder quantities and overstock flags per SKU. The 14-day free trial includes the Brand-level agent, so daily inventory alerts are on.

Start free trial →

Frequently asked questions

What is Amazon inventory management?

Amazon inventory management is deciding how much stock of each SKU to hold and when to reorder. The goal is to avoid two losses: running out, which costs sales, and overstocking, which ties up cash and can trigger Amazon storage and aged-inventory fees. The core numbers are sales velocity, supplier lead time, safety stock, reorder point and days of cover.

How do I calculate my reorder point on Amazon?

Reorder point = daily sales velocity x (supplier lead time in days + safety stock in days). Lead time runs from placing the purchase order to units being available to sell on Amazon, including production, freight and check-in. When available plus inbound units fall to that number, place the order.

How many days of inventory should I keep on Amazon?

There is no single right number. Hold enough to cover your lead time plus a safety buffer, then add the cover you want on arrival. Fast sellers with short lead times can run lean. Long lead times, launches and seasonal peaks need more. For reference, Amazon flags stock as excess above 90 days of supply and advises about two months of supply; treat that as a ceiling check, not a reorder target.

What is days of cover?

Days of cover is how many days your current stock will last at the current sales rate: (available + inbound units) divided by average daily units sold. A SKU with 520 units and 10 sales a day has 52 days of cover. Compare it with lead time, not with a fixed target.

Does Amazon have an inventory management tool?

Yes. Seller Central has FBA inventory reports and dashboards that show stock levels, inventory age and restock recommendations. They are a starting point. Check their recommendations against your own lead times and cash limits.

Can OptimalCentral order inventory for me?

No. OptimalCentral reads your FBA inventory data and suggests what to reorder and how much. It never creates shipments or places orders. You decide and you approve, because ordering spends your money.