Amazon FBA Inventory Management Guide
Why Inventory Management Matters on Amazon
Stock-outs are the most expensive inventory mistake. When your product goes out of stock, your listing becomes inactive. Your PPC campaigns pause automatically. Your organic ranking, which you built over weeks or months of sales velocity, starts declining within 24 to 48 hours. Competitors capture your customers, and some of those customers never come back. When inventory returns, you are essentially relaunching: your organic rank has dropped, your listing's sales velocity history has a gap, and you need to spend aggressively on advertising to rebuild momentum. A 7-day stock-out can take 3 to 4 weeks to fully recover from in terms of organic ranking.
Overstocking creates a different kind of pain. Amazon charges monthly storage fees of $0.56 per cubic foot from January through September and $2.40 per cubic foot from October through December. More importantly, inventory stored longer than 181 days triggers an aged inventory surcharge starting at $0.50 per cubic foot on top of regular storage fees, escalating as the inventory ages further. If you sent 2,000 units expecting to sell them in 60 days but actual velocity is half your projection, you are stuck paying escalating storage fees for months while your capital is locked up in unsold inventory.
Step-by-Step Inventory Planning
Pull your unit sales data from Seller Central's Business Reports for the past 30, 60, and 90 days. Calculate the average daily sales for each period. Use the 30-day average for short-term reorder decisions and the 90-day average for longer-term planning. If your product is trending upward, weight the 30-day average more heavily. If sales are seasonal, factor in the same period from the previous year if you have that data. For a product selling 15 units per day, you need 450 units to cover 30 days of sales.
Lead time is the number of days from when you place a reorder to when the new inventory is available for sale on Amazon. For a private label product sourced from China, total lead time typically includes production time (15 to 30 days), shipping time via sea freight (25 to 35 days) or air freight (5 to 10 days), customs clearance (2 to 5 days), Amazon check-in time (5 to 14 days after delivery to the fulfillment center), and a buffer for delays (7 to 10 days). Total lead time for sea freight is often 55 to 95 days. For wholesale sourced domestically, lead time is much shorter: order processing (1 to 3 days), ground shipping to you (3 to 7 days), prep time (1 to 3 days), and shipping to Amazon with check-in (7 to 14 days), totaling 12 to 27 days.
Your reorder point equals daily sales velocity multiplied by total lead time, plus a safety stock buffer. The safety stock accounts for demand spikes, supplier delays, and shipping disruptions. A common buffer is 7 to 14 days of additional inventory. Using the example of 15 units per day with a 75-day lead time and a 10-day safety buffer: 15 x (75 + 10) = 1,275 units. When your Amazon inventory drops to 1,275 units, place your next order. This ensures continuous availability even if production runs slightly long or shipping encounters delays.
Order enough to cover your target inventory period (60 to 90 days of sales at current velocity) minus the inventory you will have remaining when the new shipment arrives. If you sell 15 units per day and want 75 days of coverage after restocking, you need 1,125 units per order. Adjust this quantity based on supplier MOQ requirements, volume pricing breaks (ordering 1,500 units at $4.20 each instead of 1,000 at $4.80 might justify the larger order), and cash flow constraints. Do not order more than 90 days of inventory unless you have strong reason to expect a demand increase.
Check your inventory levels at least twice per week. Sales velocity changes based on seasons, competition, pricing changes, and advertising performance. A product that sells 15 units per day in March might sell 25 units per day in November as holiday shopping accelerates. Update your velocity calculations monthly and adjust reorder points accordingly. Use Amazon's Restock Inventory tool in Seller Central, which provides AI-driven recommendations for when and how much to reorder. These recommendations are a useful starting point, though they sometimes underestimate lead times for international shipments.
Understanding Your IPI Score
Amazon's Inventory Performance Index (IPI) is a score from 0 to 1000 that measures how efficiently you manage your FBA inventory. The score is calculated based on four factors: excess inventory percentage (inventory that is not selling at a reasonable rate), sell-through rate (how quickly you sell through your inventory), stranded inventory percentage (inventory in Amazon's warehouse that is not linked to an active listing), and in-stock rate (how often your top-selling products are available).
An IPI score below 400 triggers storage capacity limits, restricting how much inventory you can send to FBA. This creates a vicious cycle: limited storage capacity makes it harder to keep products in stock, which reduces sales, which can further lower your IPI. Maintaining an IPI above 500 is the minimum target, and above 600 gives you comfortable capacity headroom. Check your IPI score weekly in the Inventory Performance dashboard in Seller Central.
To improve a low IPI, focus on the biggest detractors. Fix stranded inventory immediately by resolving listing errors or creating removal orders. Reduce excess inventory through price reductions, promotions, or removal orders. Improve sell-through rates by optimizing listings and increasing advertising on slow-moving products. Maintain in-stock rates on your top sellers by keeping your reorder system disciplined. Each factor contributes to the overall score, so improvements in any area help.
Avoiding Aged Inventory Surcharges
Amazon's aged inventory surcharge applies to units stored in FBA for more than 181 days. The surcharge starts at $0.50 per cubic foot for items aged 181 to 270 days, increases to $1.00 per cubic foot for 271 to 365 days, and escalates further beyond that. These surcharges are on top of regular monthly storage fees. For a product occupying 0.25 cubic feet per unit, the surcharge is small per unit, but across hundreds of slow-moving units, it adds up to meaningful monthly costs.
Set calendar reminders to review your Inventory Age report in Seller Central every two weeks. Identify products approaching the 181-day threshold and take action before the surcharge kicks in. Options include running a promotion or coupon to accelerate sales, reducing the price temporarily to clear excess units, creating a removal order to ship inventory back to you (at $0.97 per standard unit), or creating a disposal order (at $0.32 per unit). The removal fee is almost always cheaper than months of escalating surcharges on inventory that is not selling.
Seasonal Inventory Planning
Q4 (October through December) presents unique inventory challenges. Sales volume for most product categories increases 30% to 200% compared to other quarters, requiring significantly more inventory. However, Q4 storage fees are also highest at $2.40 per cubic foot, and Amazon imposes stricter receiving limits to manage warehouse capacity. The solution is sending extra inventory in August and September, before the Q4 fee increase and receiving restrictions take effect. Our seasonal selling guide covers Q4 planning in detail.
Post-holiday inventory management is equally important. January sales typically drop 40% to 60% from December peaks. Inventory that sold briskly during the holidays may sit for months afterward, accumulating storage fees and potentially triggering aged inventory surcharges. Plan your Q4 ordering so that you sell through most of your holiday inventory by mid-January. It is better to stock out of a seasonal product in late December than to carry 3 months of excess inventory into Q1.