The Amazon FBA reorder point formula: stop stockouts and storage fees

The formula

Reorder point = average daily units sold × (lead time in days + safety days).

Lead time is everything from placing the order to units being available for sale at Amazon: production, freight, customs, any prep and receiving at the fulfillment center. Measure it from your own history, not your supplier's promise. Safety days cover delays and sales spikes; 14 to 30 days is common, more for long or unreliable supply chains.

A worked example

A product sells 12 units a day. Production takes 30 days and freight and receiving 15, so lead time is 45 days. You choose 21 safety days. Reorder point = 12 × (45 + 21) = 792 units. When total stock (at Amazon, in transit and in your own warehouse) falls to 792, place the next order. To cover 90 days of sales, order 12 × 90 = 1,080 units. Figures are fictional.

The fee for too little stock

Amazon charges a low-inventory-level fee on some FBA products when stock runs low compared with sales. Under the version effective January 15, 2026, Amazon's help page says it applies only when both the 90-day and the 30-day historical days of supply are below 28 days, calculated for each FNSKU. Keeping more than 28 days of supply at Amazon generally avoids it, and Amazon lists exemptions, including new Professional sellers for their first 365 days and products new to FBA for 180 days.

The fees for too much stock

Monthly storage fees are higher from October to December, and Amazon applies an aged inventory surcharge to units stored 181 days or longer, with steeper rates past a year. Check the Inventory Age report monthly and act on slow stock before the surcharge starts: lower the price, run a promotion or create a removal order.

Make it a weekly routine someone else runs

Put every SKU in one sheet with average daily sales, lead time, safety days, reorder point, total stock and days of supply. Each week the person running inventory updates it and flags anything at or below its reorder point; you approve the purchase order. Before ordering, check Amazon's FBA capacity limits and, in the summer, the holiday inbound cut-off dates.

Give that person their own Seller Central login through User Permissions, with only the access the task needs. Never share your own login.

Part of a store that runs without you

A reorder rule is one of five systems that let an Amazon business need a few hours a week instead of a full-time job; the others are durable products, a protected brand, written procedures with safe delegation, and a weekly owner review. No Amazon business is truly passive, but these systems get close.

Hands-Off ($9) is a 32-page guide with 7 editable templates, including this reorder planner, a role brief and permission matrix, an advertising rules sheet and a weekly owner review. Or get all three books in The Amazon Seller Series for $19. To see what your margin can carry, start with real profit per unit.