Amazon Low Inventory Level Fee: How to Avoid It in Q4
Amazon now judges stock one variant at a time. One size running thin can trigger the low inventory level fee even when the listing looks healthy. Here's the restock math that stops it before peak.
Amazon will charge you for selling too fast.
That's the Amazon low inventory level fee in one line. When a product's historical days of supply drops below 28 days in both the last 30 days and the last 90 days, Amazon adds a per-unit charge on top of your FBA fulfillment fee. And since January 15, 2026, it judges that number for each variant on its own (each seller FNSKU), not for the listing as a whole. So one size or color running thin can trigger the fee while the rest of the listing looks fine.
The fix is boring and it works: keep every variant above 28 days of supply, plan for 35, and restock your fastest-moving variant first. Below is the exact math, a worked example, and a Q4 restock plan.
What is the Amazon low inventory level fee?
Amazon launched the fee in April 2024. Its own explanation, posted by an Amazon team member in the Seller Forums post that walks through the calculation, is that thin stock stops it from spreading units across its warehouses. That slows delivery and raises shipping costs, so it bills the seller.
Here's how the rule works, straight from that post:
- Amazon measures historical days of supply: your inventory level relative to what you actually sold.
- It calculates that number over the short term (last 30 days) and the long term (last 90 days).
- It only charges the fee if both numbers are below 28 days.
- The fee is added to your FBA fulfillment fee on each unit shipped.
Amazon doesn't charge you for running out. It charges you for almost running out, and most sellers don't see it coming until the settlement report.
The formula itself is simple. Average daily inventory divided by average daily units shipped. If you hold an average of 300 units and ship 15 a day, you have 20 days of supply. Under 28. You pay.
How much does the low inventory fee cost per unit?
It depends on your size tier and how far under 28 days you fall. Amazon's fee tables sit behind the Seller Central login, so here are the published rates as broken down by AMZ Prep's low inventory fee guide (their 2025 table, check your own Fee Preview report for the 2026 number on each SKU):
| Size tier | 21 to 28 days of supply | 14 to 21 days | Under 14 days |
|---|---|---|---|
| Small standard (up to 16 oz) | $0.32 | $0.63 | $0.89 |
| Large standard (up to 3 lb) | $0.36 | $0.70 | $0.97 |
| Large standard (3 to 20 lb) | $0.47 | $0.87 | $1.11 |
The same guide reports that small and large bulky products lost their exemption on January 15, 2026, with rates running up to $2.09 per unit in the lowest supply band.
A few cents sounds like nothing. Here's the math.
Take the Smart Rodent product on our results page. On Amazon it sold at $29.95, paid $4.49 in referral fees (15%), and netted $7.73 per sale after ads and inventory. Real client numbers, not typical results, and not a promise of what your store will do. Now drop a $0.70 low inventory fee on that unit (a hypothetical, using the large standard 14 to 21 day rate). That's 9% of the net profit gone on every unit, for no reason other than the reorder went out a week late.
Why does the FNSKU change matter so much in Q4?
Before 2026, Amazon averaged days of supply across the parent product. A deep stock of mediums could quietly cover for a thin stock of larges. That cushion is gone. Amazon's 2026 fee announcement set January 15, 2026 as the effective date for the new fee schedule, and the per-FNSKU assessment is now the rule, as Inventory Hero's breakdown of the per-FNSKU change explains.
Run the math on a store like this, a hypothetical: a dog raincoat in three sizes.
- Small: sells 6 a day, averages 400 units on hand. 400 / 6 = 66.7 days of supply.
- Medium: sells 9 a day, averages 540 units. 540 / 9 = 60 days.
- Large: sells 18 a day, averages 290 units. 290 / 18 = 16.1 days.
Under the old parent-level math, you add it all up: 1,230 units / 33 a day = 37.3 days. Safe. No fee.
Under the 2026 rule, the large stands alone at 16.1 days. That's the 14 to 21 day band. At $0.70 a unit (large standard, up to 3 lb), shipping 18 a day, that's about $378 a month on one size. Stretch it across a three-month peak and it's roughly $1,134 you handed Amazon for a reorder that was three weeks short.
Average units on hand divided by units shipped per day. Fee applies under 28 days.
Here's the thing. Your best seller is the one most likely to trip the fee. It ships the fastest, so its days of supply drains the fastest. The fee lands on your winner, not your dog.
How do you calculate days of supply on Amazon before Q4?
Amazon shows it for you. Go to the FBA Inventory page in Seller Central and find the "Historical days of supply" column. Amazon's explainer says that column shows the greater of the 30-day and 90-day numbers, and you can sort it ascending to see exactly which products are closest to the fee.
But the column only tells you where you are today. Q4 is about where you'll be in five weeks, when velocity jumps and inbound slows down. So do this per FNSKU:
- Daily velocity for peak. Take your last 30 days, then lift it for the holiday bump you saw last year. If the large sold 18 a day in September and 40% more last November, plan for about 25 a day.
- Lead time to receivable. Days from purchase order to units actually live at Amazon, not just delivered to the dock. Check our Amazon Q4 2026 deadlines breakdown for the inbound dates.
- Target cover. 28 days is the cliff. Plan for 35 so a slow check-in doesn't push you over the edge.
- Reorder point. Velocity times (lead time plus target cover).
For the large raincoat at 25 a day with a 21-day lead time and 35 days of cover: 25 x (21 + 35) = 1,400 units is your reorder point. If you have fewer than 1,400 units on hand and inbound combined, the order should already be placed.
Restock the variant that sells fastest first. It's the one draining toward 28 days while you're staring at the listing total.
Can you avoid the fee without sending a mountain of stock?
Yes. And this is the part most sellers miss.
Amazon only charges when both windows are under 28 days. Its own guidance says that if a product's short-term (30-day) days of supply gets back above 28, the fee won't apply. So you don't need 90 days of perfect stock. You need a fast top-up on the thin variant so the 30-day number recovers.
The other doors Amazon has opened, per its update to the low-inventory-level fee and its calculation explainer:
- Slow sellers are exempt. Products that sold fewer than 20 units in the past 7 days don't get charged.
- New sellers and new products get a pass. New professional sellers for their first 365 days, and new-to-FBA products enrolled in FBA New Selection for 180 days.
- Amazon Warehousing and Distribution. Products auto-replenished through AWD are eligible for a fee waiver.
- Amazon-caused delays get credited. If the low stock was caused by Amazon or an Amazon-managed service, the fee is credited back by the 15th of the following month. Check your reimbursements.
I'll be honest about AWD. It solves the fee, but AWD comes with its own fees, and your cash sits in Amazon's network instead of yours. Run both numbers before you move everything over.
How is AI changing inventory planning for this fee?
Two real things, and no magic.
First, Amazon is putting more forecasting into Seller Central itself. Its 2026 announcement points sellers to the Revenue Calculator, the Fee and Economics Preview report and a Profit Analytics dashboard that shows how fee changes hit each product. And the FBA Inventory page already recommends a number of units to send for products running low.
Second, the per-FNSKU rule turned restock planning into a spreadsheet with dozens of rows. Paste your FBA Inventory export into an AI assistant and ask it to flag every FNSKU under 35 days at your peak velocity, sorted by units shipped per day. It catches the large-size problem before the settlement report does.
What AI won't do is place the purchase order for you. The fee punishes the gap between knowing and ordering.
The fee doesn't punish bad products. It punishes slow reorders on good ones.
What's the bigger picture for Amazon sellers?
Every year the fee stack gets one layer thicker. The fuel surcharge and peak fees we covered in our Amazon FBA fee changes 2026 breakdown. Placement fees. Low inventory fees. Each one is small. Together they're a slow bleed on the exact products that are working.
That's why the best Amazon sellers I talk to are doing two things at once. They tighten restock planning on Amazon so the fee never fires. And they move their winners onto a store they own, where a 15% referral fee and a pile of inventory penalties don't sit between them and the customer. On the Smart Rodent product, the Shopify version earned $78.87 net per sale at a $177.75 average order value, against $7.73 on Amazon. Our new product launch case study shows the same gap. That gap is why we wrote the Amazon fee math nobody shows you. Our Shopify vs Amazon revenue per visitor study runs the numbers side by side, and the Amazon selling guide for 2026 covers the rest of Q4, including Black Friday deal math.
Amazon rents you the shelf. Your own store is the building.
FAQ
What is the Amazon low inventory level fee? It's a per-unit charge added to your FBA fulfillment fee when a product's historical days of supply is under 28 days in both the last 30 and last 90 days.
How are days of supply calculated on Amazon? Average daily inventory divided by average daily units shipped, measured over 30 and 90 days. You'll find it in the Historical days of supply column on the FBA Inventory page.
Does the low inventory fee apply per variation? Yes. Since January 15, 2026, each seller FNSKU is judged on its own, so one thin size or color can trigger the fee by itself.
How do I avoid the Amazon low inventory level fee? Keep every variant above 28 days of supply and plan for 35. If one dips, a fast top-up that lifts the 30-day number above 28 stops the fee.
Which products are exempt? Products selling under 20 units in 7 days, new professional sellers for 365 days, new-to-FBA products in FBA New Selection for 180 days, and products auto-replenished through Amazon Warehousing and Distribution.
What to do next
Today, open FBA Inventory, sort Historical days of supply from lowest to highest, and write down every FNSKU under 35 days. Then reorder the fastest seller on that list before you touch anything else.
Book Your Profit Audit
The low inventory fee is a tax on your best sellers, and so is every other fee Amazon stacks on top of them. On a free profit audit we'll show you what your top Amazon product could earn on a store you own, and how to rebuild a high-converting product sales page in less than 15 minutes.
Or go here to check it out → revenueflows.ai
P.S. Amazon bills you when your winner runs thin. Your own store pays you when it runs hot.
Frequently asked questions
What is the Amazon low inventory level fee?
It's a per-unit charge Amazon adds to the FBA fulfillment fee when a product's historical days of supply drops below 28 days in both the last 30 days and the last 90 days. Amazon says thin stock stops it from spreading units across its network, which slows delivery and raises shipping costs.
How are days of supply calculated on Amazon?
Historical days of supply is your average daily inventory divided by your average daily units shipped. Amazon calculates it over a 30-day and a 90-day window, and you only pay the fee when both numbers sit under 28 days. You can see it in the Historical days of supply column on the FBA Inventory page.
Does the low inventory fee apply per variation?
Yes. Since January 15, 2026 the fee is assessed per seller FNSKU instead of averaging across the parent ASIN, so every size and color is judged on its own stock. A well-stocked medium can no longer cover for a large that's running thin.
How do I avoid the Amazon low inventory level fee?
Keep every FNSKU above 28 days of supply, and plan for 35 so a late shipment doesn't push you under. Amazon says that getting the 30-day number back above 28 is enough to stop the fee, so a fast top-up on your thinnest variant works.
Which products are exempt from the low inventory fee?
Amazon has exempted products that sold fewer than 20 units in the past 7 days, new professional sellers for their first 365 days, new-to-FBA products enrolled in FBA New Selection for 180 days, and products auto-replenished by Amazon Warehousing and Distribution. Seller-tool publishers also report a grocery exemption for 2026.