How to manage stock, automate reordering, and scale on Amazon

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.

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 made up of things like how fast you sell items, extra stock you have, and stranded listings.

Amazon doesn’t explain how much each part affects the score, which means you have to give it your best guess if you see it drop. End of the day, though, the main goal is to keep it above 400.

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, remove some stock–basically, 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 is stored for 181 days, costs go up. Amazon adds extra fees at 181 and 365 days, on top of regular storage charges. After a year, it’s often cheaper to remove the stock.

Sell-through rate looks at the last 90 days: units sold divided by your average stock. If it drops below 2.0, Seller Central will warn you about excess inventory. If you sell seasonally, you might go below this during slow months. That’s normal and will affect your IPI, but you still need to watch it.

If a SKU’s sell-through falls below 2.0 and it’s been in Amazon’s warehouse for 90 to 120 days, it’s time to act. Run a sale or remove some stock—it will cost you much less than waiting for the 181-day fee.

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 almost instantly. 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 stop working well around 200 products. It goes without saying (but we’ll say it anyway), a spreadsheet still works with 200 lines. However, there comes a point where the person interacting with the spreadsheet gets 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. 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.

FAQs

What is the Amazon Inventory Performance Index (IPI)?

The Inventory Performance Index is Amazon’s score for how efficiently FBA sellers are using fulfillment center storage. It draws from sell-through rate, excess inventory percentage, stranded inventory, and in-stock rate on replenished products. Sellers below 400 face storage limit restrictions, which caps how much stock they can send into Amazon’s fulfillment centers at any given time. Amazon updates IPI scores weekly inside Seller Central.

What’s the difference between stranded and excess inventory on Amazon?

Stranded inventory has no active listing to sell through. Excess inventory has an active listing but isn’t moving fast enough relative to what Amazon is holding. Stranded inventory needs a listing fix or removal order. Excess inventory needs a demand response: a price cut, promotional activity, or a removal order to rebalance stock. Applying the wrong fix to either situation wastes time and leaves the actual problem in place.

When do Amazon aged inventory surcharges apply?

Amazon applies aged inventory surcharges at 181 days and again at 365 days of FBA storage, stacked on top of regular monthly fees. For most categories, running a promotional price reduction or submitting a removal order before the 181-day mark produces a better financial outcome than absorbing the surcharge. Run the math before the clock hits, not after.

How does multichannel inventory sync work with Amazon FBA?

Multichannel inventory sync means every sale on any connected channel updates your available count across all other channels in near real-time. A unit sold on Shopify reduces your Amazon available inventory automatically, and vice versa. This keeps FBA restock decisions grounded in your actual available stock across the full operation, not just what Seller Central can see. Platforms like Linnworks connect Amazon, Shopify, eBay, and other channels into a single inventory source.

What is FBM inventory management and how does it differ from FBA?

FBM (Fulfilled by Merchant) means you store and ship your own orders instead of using Amazon’s fulfillment centers. No Amazon storage fees, no IPI score mechanics, no restock limit constraints. But FBM orders don’t automatically qualify for Prime, which can affect conversion on certain categories. Many sellers run hybrid operations: FBA for Prime-eligible fast movers, FBM for oversized or slower-moving SKUs where the FBA storage economics don’t work.