Amazon FBA inventory management and warehousing: IPI, storage, and restock limits

Amazon doesn’t warn you before you hit a storage limit. One week you’re preparing to restock, and the next, Seller Central says you have no space left. If your IPI score drops below 400, the problem has likely been growing for a while.

How the score works is fairly simple. The problems that cause it to drop are not. Sell-through rate, extra stock, and stranded listings can all reduce your restock limits if you don’t watch them. But if you manage these well, your score will improve on its own.

However, add a second, third, or fourth sales channel and the same inventory errors get harder to catch.

What is an FBA warehouse?

An FBA warehouse is an Amazon fulfillment center where Amazon holds your inventory under Fulfillment by Amazon. You ship your stock there, and Amazon stores it, picks, packs, and ships each order, and handles customer service and returns. Amazon may split an inbound shipment across several fulfillment centers, and you pay for that storage. For the full picture of how FBA works, see our Amazon FBA guide.

How FBA warehousing costs work

• Monthly storage fee. Charged per cubic foot, and higher from October through December.
• Storage utilization surcharge. Added when the volume you store is high compared with your recent sales.
• Aged inventory surcharge. Charged on stock that sits for 181 days or more, and it rises in bands as the stock gets older.
• Low-inventory-level fee. Charged when you hold too little stock for your sales.
• Inbound, removal, and disposal fees. Charged when you send stock in and when you take it out or dispose of it.

Amazon changes these rates regularly, so check Seller Central for current numbers. Our guide to Amazon FBA fees covers the main fees, and the reports in Seller Central show what you pay for each product.

Storing inventory outside FBA warehouses

You don’t have to hold all of your stock in FBA. Amazon Warehousing and Distribution (AWD) is a bulk storage service that can replenish your FBA stock, and inventory held there doesn’t count against your FBA storage volume. You can also keep stock in your own warehouse or with a 3PL and send it to Amazon in smaller shipments. See our comparison of Amazon FBA vs 3PL, and our guide to FBA vs FBM if some products don’t suit FBA storage.

Your IPI score is a restock limit in disguise

Most FBA sellers know about the 400 IPI limit.

The problem is the score changes slowly, so you might not notice it dropping during your weekly checks. By the time it falls below 400, Amazon has already reduced your storage space. Now you have to fix an issue that began weeks ago.

Your score is built from four things: your sell-through rate, how much excess inventory you hold, stranded inventory, and the in-stock rate on products you replenish. Amazon updates it every week. The main goal is to stay above 400, and a buffer of 500 or more protects you from a short dip.

If your score goes below 400, Amazon reduces your storage space. Less space means you can keep less stock, so you’re more likely to run out. This lowers your sales and keeps your score low. Once this cycle starts, it can get worse fast.

Storage isn’t the only problem. You need to clear space by moving or removing extra stock and fixing stranded listings. Most sellers know this, but many wait too long instead of catching the problem early.

Stranded vs. excess inventory

Confusing these two can make you spend a week fixing the wrong problem.

Stranded inventory means your stock is in an Amazon warehouse, but there’s no active listing to sell it. This can happen if a listing is deleted, an ASIN is suspended, or there’s a rules problem. The items just sit there, costing storage fees, but no one can buy them. You need to fix the listing, ask for removal, or have the items thrown away.

Excess inventory is a different problem. Your listing is active and selling, but not fast enough for how much stock you have in Amazon’s warehouse. In other words, you sent in too much. The solution is to create more demand. Lower the price, bundle it with a faster-selling item, or remove some stock. Find a way to move the item.

If you’ve been changing the listing but your stock isn’t selling, you’re likely working on the wrong problem.

Sell-through rate and the aged inventory clock

Once your inventory has been stored for 181 days, costs go up. Amazon’s aged inventory surcharge starts at day 181 and rises in bands as the stock gets older, with the highest rates past 365 days. Amazon’s seller forum lists $0.50 per cubic foot for stock aged 181 to 210 days and $5.90 per cubic foot for 331 to 365 days, effective January 16, 2026. These come on top of regular storage charges, so it’s often cheaper to remove old stock than to keep it. See Amazon FBA fees explained for the other fees.

Sell-through rate looks at the last 90 days: units shipped divided by your average stock on hand. If you sell seasonally, it may fall during slow months. That’s normal and will affect your IPI, but you still need to watch it.

If a SKU has been in Amazon’s warehouse for 90 to 120 days and its sell-through is low, it’s time to act. Run a sale or remove some stock. It will cost you much less than waiting for the 181-day surcharge.

The in-transit trap

Counting inventory that’s on the way as available is a big reason sellers order too much with Amazon’s fulfillment. Delivery times can change depending on the warehouse, season, or how you prepared your shipment. If there’s a delay and your available stock hits zero before the new items arrive, you run out of stock. Your reorder alert, based on total inventory (including in transit), didn’t come soon enough.

Keep in-transit inventory separate from what’s in Amazon’s warehouse and ready to ship. Set your reorder point based only on what’s available there, plus add extra time for supplier delivery and Amazon’s receiving process.

“Managing Amazon FBA Inbound Shipments in Linnworks is a big time saver. It keeps our stock more consistent and gives us accurate stock availability, both because it’s easier for us to book FBA shipments, but also when stock comes in it’s all automatic.”

Simon Hurley, Managing Director, Rothko & Frost

When Amazon isn’t your only channel

A sale on Shopify doesn’t match your Amazon restock schedule.

Sell three units on your website and your Amazon inventory tool or spreadsheet won’t update right away. Your stock count in Amazon’s warehouse stays wrong until someone updates it, which could take hours or days. Multiply that across all your products and sales channels, and it becomes a real problem. According to the Linnworks 2026 State of Commerce Operations report, 29% of retailers say syncing inventory across channels is a big challenge. Only about a third of UK and US retailers have good inventory visibility. The rest know they have gaps but usually ignore them.

Helium 10, SoStocked, and InventoryLab work well if you only sell on Amazon. But if you add Shopify, eBay, or wholesale, you have to manage inventory across platforms those tools can’t connect. That’s where multichannel platforms like Linnworks can help. They keep one stock count per product and update it everywhere within minutes. Linnworks syncs stock across 100+ native channel integrations in under 10 minutes, so a sale anywhere updates your inventory everywhere.

If you only use FBA and no other stores, a full multichannel platform might be more than you need. But once you add more sales channels, it becomes much more useful.

The spreadsheet ceiling

Spreadsheets work for a small catalog, but they get harder to trust as it grows. There comes a point where the person using the spreadsheet is overwhelmed by the data.

Tracking sales per product, adjusting for supplier delivery times, and recalculating reorder points after stockouts or sales gets overwhelming quickly. Even if the spreadsheet is up to date, no one really trusts it. And if you don’t trust your reorder numbers, you’re much more likely to run out of stock as your business scales.

The Replenishment Report shows which products are close to their reorder points, using real sales data and supplier delivery times. You can create purchase orders right in the platform. See how to fulfill FBA with the Replenishment Report. For teams used to weekly spreadsheet checks, this saves a lot of time on calculations and double-checking, especially when no one trusts the numbers.

If you sell on two or more channels and still update inventory by hand, it will only get harder as you grow. Request a demo to see how this system could work for your mix of sales channels.

If you’re using Amazon to fulfill your orders, read our complete guide to Amazon FBA to learn more ways to improve inventory and fulfillment performance.

FAQs