Amazon FBA inventory and restock planning: how to stay in control of limits and aged-inventory surcharges

Your restock limit is not an inventory problem, it is a data problem. Amazon decides how much you can send in based on your IPI score and your sell-through speed per ASIN, and if you do not have that in one view alongside your own warehouse, you plan blind.

Short answer. Your restock limit is tied to your IPI score: below 400 Amazon caps your storage space, from 500 you get more generous limits. On top of that there is a product-level limit per ASIN based on sell-through speed. Send smaller, more frequent shipments based on actual sales and plan FBA inventory together with your own stock, not separately.

How restock limits and your IPI score connect

The Inventory Performance Index is a rolling 12-week average of four factors: your excess inventory percentage, your stranded inventory percentage, your sell-through rate and your in-stock rate. Below the threshold of 400, Amazon imposes storage limits on you. Above 400 you are exempt for standard and oversized storage, and from 500+ you get noticeably more room.

But the account-wide limit is only half the story. On top of it sits a product-level limit per ASIN, based on how fast that specific product sells. A top seller you can keep replenishing, a slow SKU hits a wall. Anyone who looks only at the account limit does not see why a specific shipment gets rejected.

You find your current limits in the Inventory Performance Dashboard and in the Shipping Queue. Those numbers change weekly, usually on Monday or Tuesday. Planning on a screenshot from last week is planning on stale data.

Aged-inventory surcharges have ramped up faster since January 2026

This is where it gets expensive. Since January 16, 2026, the aged-inventory surcharges start 90 days earlier, namely from 181 days instead of 271. The tier schedule per Amazon Seller Central climbs to a new tier from 456 days:

• 181-210 days: $0.50 per cubic foot
• 271-300 days: $5.45 per cubic foot
• 331-365 days: $5.90 per cubic foot
• 366-455 days: $6.90 per cubic foot or $0.30 per unit, whichever is higher
• 456+ days: $7.90 per cubic foot or $0.35 per unit

The surcharge is assessed monthly on the 15th and charged around the 18th to 22nd, on top of your regular storage costs. That means slow inventory you will "sell eventually" quietly drains you every month. And that does not even count stranded inventory: stock whose listing has been removed for some reason, so customers cannot find it and you do not sell. You have to resolve that within 30 days, otherwise it counts toward your IPI and the costs pile up.

The mistake is almost never sending in too little

When I sit in with a scaling seller, the problem rarely lies with the limit itself. It lies with the calculation underneath. The reorder points run on gut feeling, sell-through speed per ASIN is not factored in, and FBA inventory and your own warehouse sit in two separate systems. Then you send in too much of your slow SKUs (aged-inventory surcharge) and run out of stock on your fast movers (lost revenue and a falling sell-through rate, which pulls your IPI down again).

I run through your process first before I build anything. Stages that have grown over time can often be done smarter or dropped entirely. The three-step approach I stick to:

1. Goal. One view where, per ASIN, your daily sales, your FBA inventory, your own stock and your restock limit sit side by side. Numbers that add up, less manual work.
2. Process. Which manual steps do you run now, and which of those are leftovers from a previous phase that you can simply scrap?
3. Building the smarter solution. Where a standard tool does not cover your situation.

Where the standard tool stops and building begins

Let me be honest about build-vs-buy. Tools like Sellerboard, Helium 10 and RestockPro cover the happy path excellently: one marketplace, standard SKUs, predictable sales. For many sellers that is enough, and I say so too.

It pinches the moment your reality deviates from that happy path. You sell on Amazon and bol and your own webshop, and you want to plan inventory across those channels together, not three times separately. You have bundles, multipacks or seasonal peaks that the standard forecast does not understand. You want to link your FBA restock signals to your purchasing at the supplier or to your own WMS. That is exactly the part where an out-of-the-box tool stops and where I build the integration, the dashboard or the AI workflow that fits your exceptions.

The calculation has to happen either way. Restock on sell-through speed, not on feeling. Smaller, more frequent shipments so your sell-through stays high and you are not stuck with aged-inventory surcharges for months. The difference is whether you do that calculation by hand in a spreadsheet or whether it is ready automatically every morning with data from last night.