Restock planning for Amazon FBA: how many days of stock to keep

There is no single correct number of days of stock for every Amazon product. A locally made item that can be replenished in a week needs a different plan from an imported item with months of production and transit time. Start with the time until replacement units become sellable.

The useful question is: how much demand must the business cover before the next reliable replenishment arrives? Then decide which units belong at FBA, at a warehouse, and with your supplier. This guide uses a simple planning example, not an Amazon inventory requirement.

Measure demand without hiding stockouts

For each SKU, record recent unit sales and the number of days it was actually available. Divide units by in-stock selling days to estimate daily demand. If a product sold 300 units during 25 available days, that is 12 units per available day, not ten units across a thirty-day calendar.

That adjustment is only a starting point. Demand can change when the product returns to stock, ads restart or competitors change their prices. Compare recent demand with a longer period. Note promotions, holidays, one-off orders and changes in selling price rather than quietly averaging them together.

Use a base case and a higher-demand case if the range is meaningful. Keep the assumptions visible. A new product with little history needs a smaller, more frequent review cycle and an explicit cash limit, rather than a forecast presented as certainty.

Count inventory by its real state

Sellable FBA stock can fulfill orders now. Unsellable, stranded or reserved units may not be available when you need them. Check their actual status instead of adding every unit in Seller Central to available stock.

Keep separate columns for sellable FBA units, sellable warehouse units, confirmed inbound shipments and open supplier orders. Add dates and confidence levels to inbound quantities. A purchase order with no production date is not the same as a shipment with a confirmed arrival plan.

Avoid double counting. Units that leave your warehouse and become an inbound shipment must move between columns. They do not remain in both. Amazon's inventory management guide describes the broader role of demand forecasting, replenishment and inventory visibility.

Build the full lead time

Lead time begins when you need to commit the order and ends when the units can sell. Include supplier processing, production, inspection, freight booking, transit, customs where relevant, warehouse handling, FBA preparation and Amazon receiving.

Ask for dates based on recent shipments, not only a supplier's fastest advertised estimate. Separate normal lead time from a delay allowance. A useful worksheet shows the expected days for each stage and who can confirm them.

In our arithmetic example, production takes 20 days, freight and preparation take 15 days, and receiving takes ten days. Total replenishment lead time is 45 days. Those are made-up inputs for this example. Replace every one with your own evidence.

If you review orders only once a week, the product can cross its reorder point between reviews. Include that review interval in the planning horizon or monitor the trigger more often. Do not assume a weekly spreadsheet behaves like a daily alert.

Calculate a reorder point

For steady demand, a simple starting formula is:

Reorder point = daily demand × lead-time days + safety stock.

Suppose daily demand is ten units, lead time is 45 days, and you choose a fifteen-day demand buffer. Lead-time demand is 450 units. Safety stock is 150 units. The reorder point is 600 units of inventory position.

Inventory position usually means sellable stock plus confirmed units on order, less commitments not already reflected in your stock count. Define it once and use the same definition each week. Check arrival dates too: an order arriving after a projected stockout cannot prevent that gap.

The fifteen-day buffer in this example is a management choice, not a universal recommendation. Review your own demand variation and shipment delays. A fragile supplier, a seasonal peak or a costly stockout can justify a different buffer. Extra stock also ties up cash and can create storage or disposal costs.

Separate the trigger from the order quantity

The reorder point tells you when to act. It does not tell you how much to buy. Choose an order quantity based on your desired coverage after the shipment arrives, your order review schedule, minimum order quantities and available cash.

For a periodic review plan, one simple approach is:

Order-up-to level = daily demand × (lead time + review interval + safety days).

If demand is ten units, lead time is 45 days, reviews are seven days apart, and safety cover is fifteen days, the order-up-to level is 670 units. If reliable inventory position is 420 units, the suggested order is 250 units before adjusting for case packs or a minimum order.

Round thoughtfully. A supplier minimum of 1,000 units would change this example substantially. Compare alternate suppliers, staggered releases or a warehouse arrangement before buying months of extra stock just to satisfy a spreadsheet formula.

Decide how much belongs inside FBA

A business might need long overall supply coverage without sending all of it to FBA at once. Warehouse stock and planned replenishments can support smaller FBA deliveries if the transfer process is dependable.

Compare storage, placement, handling and transfer costs with the risk of being unable to replenish. Review current capacity limits and applicable fees in your own marketplace. Amazon policies and fee rules can change. Use current account information rather than treating a remembered days-of-supply threshold as a universal rule.

Also check cash timing. You may pay a deposit today and a balance before shipment, then wait for receiving, sales and disbursement. A profitable product can still create a cash shortage while several orders overlap.

Review the plan every week

Keep one row per SKU with daily demand, sellable units, dated incoming stock, lead time, safety stock, reorder point, proposed quantity and owner. Add a projected stockout date and the next believable arrival date. Review exceptions first.

After each shipment, compare expected and actual stage dates. After a promotion, compare forecast and actual demand. Update the inputs when the evidence changes. A simple plan that gets maintained is more useful than a complex forecast nobody trusts.

Want help finding stock risks alongside your margins and ads? Get a free BrimScout profit audit. We can start with the products and assumptions that need attention first.