Amazon Inventory Restock Planning: Formulas for FBA

Amazon inventory restock planning means working out when to reorder and how much, so stock arrives before you run out without overpaying for storage. The core formula is simple: reorder point = average daily sales × total lead time + safety stock. Total lead time includes production, freight and Amazon's receiving time. In 2026 you also have to fit within your FBA capacity limit and keep enough days of supply to avoid the low-inventory-level fee.

Key takeaways

• Calculate daily sales velocity from in-stock days only, or stockouts will drag your forecast down.
• Count the whole lead time: production, freight, prep and Amazon receiving, not just shipping.
• Hold safety stock for demand swings and delays. It costs less than a stockout.
• Keep FBA days of supply above 28 to avoid the low-inventory-level fee, but not so high that storage and aged inventory fees bite.
• Q4 needs its own plan: higher demand, slower receiving and October–December storage rates.

Why restock planning matters on Amazon

Running out of stock costs more than the lost sales. While you're out, competitors pick up your buyers, your organic rank can slip and your ads stop serving. Getting back to where you were often takes extra ad spend.

Overstocking costs money too. Amazon charges monthly storage by the cubic foot, adds surcharges for aged inventory, and may limit how much you can send. The goal is the middle ground: enough stock to never run out, and not much more.

The five numbers you need

1. Daily sales velocity

Use the last 30 to 90 days and divide units sold by days in stock, not calendar days.

Say you sold 900 units in the last 30 days but were out of stock for 7 of them. Velocity is 900 ÷ 23 = about 39 units per day, not 30.

Then adjust for what's coming: seasonality, a planned price change, a deal, or a new ad campaign. Last year's same-month data is the best guide for seasonal products.

2. Total lead time

Add every step:

• Production: e.g., 30 days
• Freight to the US, including customs: e.g., 35 days by sea
• Prep and labelling: Amazon ended its own FBA prep and item labelling services in the US on 1 January 2026, so your supplier or a prep centre has to handle this. Add their time.
• Amazon receiving: from delivery to units being available, often a week or more, and longer in Q4.

Use your real history, not your supplier's best case.

3. Safety stock

There are two common ways to set it.

Simple days-based buffer: hold a fixed number of days of sales, for example 14 to 30 days. Easy to use and covers both demand and delay risk.

Statistical formula: safety stock = Z × σ × √L, where:

• Z = service level factor (1.65 for about 95% in-stock, 2.05 for about 98%)
• σ = standard deviation of daily sales
• L = lead time in days

This only covers demand swings, not supplier or shipping delays. Many sellers use the larger of the two methods.

Worked example: when and how much to reorder

Say you sell a pillow with these numbers:

• Velocity: 40 units per day
• Lead time: 30 days production + 35 days freight + 10 days receiving = 75 days
• Standard deviation of daily sales: 10 units
• Available at Amazon: 2,800 units
• Inbound: 600 units
• Target: stock should last 60 days after the new order arrives

Safety stock

• Statistical: 1.65 × 10 × √75 = 1.65 × 10 × 8.66 ≈ 143 units
• Days-based (14 days): 14 × 40 = 560 units
• Use the larger: 560 units

Reorder point

40 × 75 + 560 = 3,560 units

You have 2,800 + 600 = 3,400 units on hand and inbound. That's below 3,560, so reorder now.

Order quantity

Units needed = velocity × (lead time + coverage) + safety stock − (available + inbound) = 40 × (75 + 60) + 560 − 3,400 = 5,400 + 560 − 3,400 = 2,560 units

Round up to your supplier's carton quantity.

You don't have to send all 2,560 units to Amazon at once. Many sellers keep part of the order in a 3PL or Amazon Warehousing and Distribution (AWD) and send smaller FBA shipments every few weeks. That keeps FBA days of supply healthy without paying FBA storage on months of stock.

Using Amazon's Restock Inventory tool

Seller Central gives restock suggestions based on your sales and inbound shipments. Go to Inventory > FBA Inventory and open the restock view (in some accounts it's under Inventory > Inventory Planning > Restock Inventory). For each SKU you'll see days of supply, an alert, a recommended replenishment quantity and a recommended ship date. The same data is available as a downloadable restock report.

To make it more useful:

• Set your real supplier lead time and target days of cover in the restock settings. The defaults rarely match your supply chain.
• Check the Minimum Inventory Level that Amazon shows for each product. It's Amazon's estimate of the least stock you should keep at fulfillment centers.
• Override it for known events, such as deals, launches, price drops or seasonal peaks. The tool looks backwards.

2026 rules that shape your restock plan

Capacity limits

Amazon sets a monthly FBA capacity limit for each storage type, measured by volume. On-hand inventory and inbound shipments both count against it. The next month's limit is announced in the third full week of the month, with estimates for the two months after. Your IPI (Inventory Performance Index) score is one factor, along with your sales forecast, shipment lead time and fulfillment center space. You can find your limits in the Capacity Monitor on the FBA Inventory page. If you need more room, Capacity Manager lets you request extra capacity by offering a reservation fee per cubic foot.

Plan your shipments to fit the limit. If your order is bigger than your space, stage it upstream.

Low-inventory-level fee

Amazon charges a per-unit fee on FBA shipments when both your 30-day and 90-day historical days of supply fall below 28 days. From 15 January 2026 it's measured per FNSKU (Amazon's fulfillment barcode for each SKU), so one low-stock variation can trigger it even if the parent looks healthy, and it now applies to bulky items. Exemptions include new sellers, products new to FBA and low-volume products. Check Seller Central for current rates. Our inbound placement and low-inventory fee guide covers it in detail.

In the example above, 2,800 available units ÷ 40 per day = 70 days of supply. Comfortably safe. At 1,000 units you'd be at 25 days and at risk.

Storage and aged inventory

Monthly storage is $0.78 per cubic foot for standard-size items from January to September and $2.40 from October to December. Oversize is $0.56 and $1.40. Aged inventory surcharges apply on top for stock that sits too long.

Say each pillow takes 0.15 cubic feet and you hold 3,000 units at Amazon:

• 3,000 × 0.15 = 450 cubic feet
• January–September: 450 × $0.78 = $351 per month
• October–December: 450 × $2.40 = $1,080 per month

That's why Q4 stock should sell through quickly. Read more in our storage fees and aged inventory guide, and check per-unit costs with the FBA Profit Calculator.

Inbound placement fee

When you create a shipment with Send to Amazon, you can choose how many fulfillment center locations to ship to. Sending to fewer locations usually means a per-unit inbound placement fee; splitting across more locations usually lowers or removes it but adds freight work. Compare the options on each shipment, and factor the fee into your landed cost.

Planning for Q4 2026

Holiday peak fulfillment fees apply from 15 October 2026 to 14 January 2027, and they stack with the 3.5% fuel and logistics surcharge. Our holiday peak fees guide has the details. For restocking:

1. Forecast with last year's November and December velocity, adjusted for growth.
2. Add receiving buffer. Fulfillment centers slow down in peak, so allow extra days.
3. Check Amazon's inbound cutoff dates for Prime Big Deal Days and Black Friday in Seller Central.
4. Plan the January exit. Aim to finish the season with normal stock levels, not three months of excess.

Common restock mistakes

• Calculating velocity over out-of-stock days. You'll under-order and stock out again.
• Using shipping time as lead time. Production, prep and receiving often double it.
• No safety stock. One late container and you're out.
• Sending everything to FBA. You pay peak storage and may hit your capacity limit.
• Forgetting variations. With FNSKU-level fees, every size and colour needs its own plan.
• Trusting the restock tool blindly. It doesn't know about your promotions or supplier delays.

Bottom line

Restock planning comes down to three numbers: daily velocity from in-stock days, honest total lead time and enough safety stock. Reorder when on-hand plus inbound falls below velocity × lead time + safety stock, then send stock to FBA in waves that fit your capacity limit and keep you above 28 days of supply. Plan Q4 separately, because demand, receiving times and storage rates all change.

Frequently asked questions

Amazon fees, policies and features change often. Figures here were checked in October 2026; confirm current rates in Seller Central before making pricing or budget decisions. Sotrics is not affiliated with Amazon.