Amazon FBA Low-Inventory-Level Fee: How Days of Supply Triggers Costs

What the Low-Inventory-Level Fee Is (and Is Not)

In a Seller Forums explanation, Amazon said the fee exists because low inventory relative to demand makes it harder to place products across the fulfillment network, which can slow delivery and raise shipping costs. The charge is added to the FBA fulfillment fee for shipped units of eligible products.

Amazon calculates the fee from historical days of supply: inventory levels relative to actual historical sales. That is different from long-term storage fees, which apply when inventory ages in the network. Our guide to avoiding long-term storage fees covers the aging-inventory side. This post is only about the understocked side.

Amazon also said it will only charge the fee when historical days of supply is below 28 days, and only when both the short-term measure (last 30 days) and the long-term measure (last 90 days) are below that line. If either window is at 28 days or above, the fee does not apply. That gives you two ways out: improve short-term stock quickly, or manage inventory so the 90-day picture stays healthy.

How Historical Days of Supply Is Calculated

In Seller Forums answers, Amazon described historical days of supply as average daily inventory units on hand divided by average daily shipped units, measured over both the last 90 days and the last 30 days.

Amazon's forum walkthrough used a sample product where the short-term figure was below 28 days but the long-term figure came out to 42.0 days. That product would not incur the fee, because both windows must be under 28 days. The same logic applies in reverse: a thin week does not trigger the fee if the 90-day average is still above the line.

On the FBA Inventory page, Amazon shows a Historical days of supply column. Amazon said that column displays the greater of the short-term and long-term metrics. If that displayed value is greater than 28, the fee is not applied. You can hover the details link to preview the calculation for a product, search by SKU or ASIN, and sort the column ascending to find products closest to the fee.

Inbound units typically do not count until they are received as sellable inventory, and the metric may update weekly. Plan replenishment with that lag in mind.

Parent ASIN vs FNSKU: What Amazon Said, and What Changed for 2026

Amazon's original Seller Forums explanation said historical days of supply was calculated at the parent-product level, so variations under the same parent shared the metric. In a later Seller Forums reply about fluctuating fulfillment fees, Amazon staff also described calculating the metric at the product FNSKU level and adding the fee to FBA fulfillment for shipped units of eligible products.

Secondary fee trackers (including Goat Consulting) describe a January 15, 2026 update: calculation at seller-FNSKU level, coverage for small and large bulky as well as standard-size, and a Grocery exemption. Goat also publishes example 2026 rates by size tier and days-of-supply band (for example, small standard listed from $0.32 in the 21 to under-28-day band up to $0.89 in the 0 to under-14-day band). Treat those dollars as secondary and confirm the live rate card in Seller Central.

Amazon's 2026 U.S. Referral and FBA fee update said FBA fees would rise by an average of about $0.08 per unit, that no new fee types were introduced, and that changes were generally effective January 15, 2026.

Which Products Are Eligible, and Who Is Exempt

Amazon's Seller Forums FAQ stated that the fee applies to standard-sized products when both long-term and short-term historical days of supply are less than 28 days. Later Seller Forums posts quoting current help text also list Small and Large Bulky products under the same 28-day rule. Always open the current help article in Seller Central for the size tiers that apply to you today.

Amazon listed these exemptions in that same FAQ:

• New Professional sellers for the first 365 days after the first inventory-received date.
• New-to-FBA parent products for the first 180 days after the first inventory-received date, if you are enrolled in the FBA New Selection program.
• Products auto-replenished by Amazon Warehousing and Distribution (AWD). Later help-text quotes on the forums describe a more specific AWD rule: SKUs where 70% or more of inventory was auto-replenished through AWD over the prior 90 days.

Secondary sources also report a Grocery category exemption after the January 2026 updates. If you sell Grocery, verify that exemption on Amazon's current help page rather than relying on a third-party summary alone.

Where to See It in Seller Central

Amazon pointed sellers to the FBA Inventory page:

1. Open FBA Inventory in Seller Central.
2. Find the Historical days of supply column (greater of the 30-day and 90-day metrics).
3. Hover the details link for the calculation preview on a given product.
4. Sort ascending to surface SKUs under or near 28 days.
5. Use Amazon's recommended send-in quantities on that page when inventory is low.

When fulfillment fees look higher than expected, check Payments > Transaction View. The low-inventory-level fee is added to the fulfillment line for shipped units. If lost or damaged stock drove you under the line, see our guide to FBA reimbursements.

How to Avoid or Minimize the Fee

Amazon's own advice is straightforward: for products you replenish yourself, send enough additional units that the product's short-term (last 30 days) historical days of supply exceeds 28 days. When the short-term metric clears 28 days, the fee does not apply, even if the long-term metric is still below.

Practical habits that match that rule:

• Set a reorder point above 28 days of cover based on your recent sell-through, plus inbound lead time and receiving lag. Our reorder point formula post is useful here, as long as you also stay clear of aged-inventory surcharges.
• Check FBA Inventory weekly and sort by historical days of supply. Catch SKUs drifting under 40 days before they cross 28.
• Watch velocity spikes from promos, seasonality, or viral demand. A SKU that suddenly ships faster can burn through cover before your next shipment arrives.
• Confirm exemptions if you are a new Professional seller, launching a new-to-FBA parent under New Selection, or using AWD auto-replenishment.
• Model the fee in your unit cost with Amazon's Revenue Calculator or your own sheet. Our FBA fee calculator guide helps you see the full per-unit picture.

Amazon and secondary sources describe the fee as tiered by how far below 28 days you sit (deeper shortages cost more). Forum answers summarized bands such as 0–14 (highest), 14–21, and 21–28 (lowest), with no fee above 28. Confirm exact dollars in Seller Central.

Putting It Together

The low-inventory-level fee is Amazon's charge for running too lean for too long relative to your own sales history. It is not a long-term storage fee, and it is not automatic every time your on-hand count looks low for a day or two.

The key takeaways:

• The fee applies only when both 30-day and 90-day historical days of supply are below 28 days
• Historical days of supply is average daily inventory divided by average daily shipped units
• See it on the FBA Inventory page; the column shows the greater of the two windows
• Amazon exempts new Professional sellers (365 days), New Selection new-to-FBA parents (180 days), and AWD auto-replenished SKUs under the stated rules
• Restock so the short-term metric clears 28 days; verify 2026 size-tier and FNSKU rules and rates in Seller Central

Your next step: Open FBA Inventory, sort Historical days of supply ascending, and pick every SKU under 40 days. For each one under 28, create or accelerate an inbound shipment sized to push the 30-day metric back above the line, then re-check after the weekly metric update.