Amazon FBA Inventory Planning: How to Never Run Out of Stock

Running out of stock on Amazon is one of the most expensive mistakes a seller can make. When an ASIN goes out of stock, it loses ranking momentum and can take weeks to recover. Proper inventory planning prevents stockouts and keeps your listings performing.

The basic inventory formula

Reorder Point = (Average Daily Sales × Supplier Lead Time) + Safety Stock

Example: If you sell 10 units per day and your supplier takes 30 days to manufacture and ship, your reorder point is 300 units. Add safety stock — typically 15-30 days of additional supply — and you reorder when stock drops to 450-600 units.

Calculating average daily sales

Pull your unit sales from the Business Reports section in Seller Central. Use a 90-day average to smooth out weekly variation. If your product is seasonal, use the equivalent period from last year as a reference for seasonal adjustments.

Supplier lead time

Lead time = manufacturing time + shipping transit time + FBA processing time. Manufacturing is typically 15-30 days for most consumer goods. Ocean shipping from China takes 20-40 days. FBA check-in takes 3-7 business days. Total lead time is often 40-75 days.

Build in buffer. Suppliers often ship late. Add 20% to your supplier's stated lead time.

Safety stock

Safety stock is inventory held to cover demand spikes and supply delays. A common rule of thumb is 30 days of safety stock for stable products, 45-60 days for products with volatile demand (seasonal items, products prone to viral traffic).

FBA storage limits

Monitor your IPI score and storage limits monthly. If Amazon reduces your storage limit, you may not be able to send as much inventory as your planning model calls for. Plan FBA shipments 3-4 weeks ahead to give yourself time to react to limit changes.

For FBM sellers

FBM inventory planning is simpler because inventory is in your own warehouse. The key variable is shipping processing time rather than FBA check-in time. Monitor order volume trends weekly and reorder when stock drops to 30 days of supply plus your supplier's lead time.

Tools for inventory planning

Seller Central's Restock Inventory report generates suggested reorder quantities based on your sales velocity and lead times. It is a good starting point but may not account for planned promotions or seasonal spikes — supplement it with your own calculations.

More sophisticated sellers use standalone inventory planning software (RestockPro, SoStocked, Skubana) that integrates with Seller Central and provides more detailed forecasting.