Amazon's low-inventory-level fee: the 28-day rule, the 2026 FNSKU change, and a reorder trigger that survives both

Key takeaways

• The fee applies only when a product's historical days of supply is below 28 on BOTH the short-term (last 30 days) and long-term (last 90 days) measure. If either window is at 28 or above, no fee. That is Amazon's published rule.
• Since January 15, 2026 the metric is calculated per seller-FNSKU, not per parent ASIN, and small-bulky and large-bulky products are now in scope. Grocery is exempt.
• It is charged per unit shipped while you are under the line, on top of the normal fulfillment fee. Published 2026 rate cards put standard-size bands at roughly $0.32 to $1.11 per unit and bulky up to about $2.09; the exact figure for your tier is on the low-inventory-level fee page in Seller Central.
• Exemptions worth checking before you panic: your first 365 days on FBA, the first 180 days of a new parent ASIN, products that shipped fewer than 20 units in the trailing 7 days, and FNSKUs auto-replenished from Amazon Warehousing and Distribution.
• The fix is a reorder trigger that includes supplier, transit, customs and Amazon check-in time on top of the 28 days — because the fee is charged during the replenishment gap, not after it.

Twenty-eight days. That is the threshold, Amazon publishes it, and Seller Central shows you the metric for every FNSKU you own. The fee switches on only when both the 30-day and the 90-day historical days of supply sit under that line. An earlier version of this guide hedged on the number because third-party rate cards disagreed with each other. Some of them were simply wrong. Amazon is not.

01How the metric is calculated

Historical days of supply is the number of days your available FBA inventory would have lasted at your recent shipping rate:

historical days of supply = average daily units available ÷ average daily units shipped

Amazon computes it over two windows and applies the fee only when both fall below 28:

Window	Period measured	Fee applies if…
Short-term	Last 30 days	below 28 days and
Long-term	Last 90 days	below 28 days

The two-window design is your escape hatch. A SKU that dipped to 20 days of supply in the last month but averaged 35 days over the quarter is not charged. The fee lands on products that have been thin for a sustained period.

02What changed on January 15, 2026

Two structural changes, both in Amazon’s 2026 US fee update:

1. Per-FNSKU measurement. The metric was previously assessed at parent-ASIN level. It is now assessed for each seller-FNSKU. A ten-variant listing with one thin color used to be protected by the healthy siblings. Now that color is charged on its own sales, and the other nine are not. This is better targeted than the old rule, but it means your slowest variant sets its own exposure.
2. Bulky products are in scope. Small bulky and large bulky size tiers were exempt before 2026. They are not now, and their rate bands are the highest on the card.

Grocery remains exempt. Dangerous goods follow the standard bands.

03Where to read it in Seller Central

Don’t estimate days of supply from your own spreadsheet. Read Amazon’s figure. Amazon’s figure is the one it bills on.

Seller Central > Inventory > FBA Inventory — the table has a Historical days of supply column. Sort ascending. Anything under 28 is being charged now; anything between 28 and about 40 is your watch list. Use the column filter to show only rows under a threshold rather than scrolling the catalog.

Seller Central > Reports > Fulfillment > Payments > Fee Preview — shows the estimated fee per FNSKU at current supply.

Seller Central > Reports > Payments > Transaction View — filter by Service fee and search for “low-inventory” to see what you have actually paid, per unit, per SKU. Pull ninety days of this before changing anything. Sellers routinely find the fee is either far larger than they assumed or immaterial, and those two situations need different responses.

04What it costs

The fee is tiered by how far under 28 days you are: deeper shortage, higher band. Published 2026 rate cards (secondary sources, listed below) put the standard-size bands between about $0.32 and $1.11 per unit and bulky bands up to about $2.09. The card itself lives on the low-inventory-level fee help page in Seller Central; treat the figures here as the shape of the fee, not the invoice.

The share of price is what matters:

Selling price	Fee at $0.65	Fee at $1.11	Share of price at $1.11
$12	$0.65	$1.11	9.3%
$20	$0.65	$1.11	5.6%
$35	$0.65	$1.11	3.2%
$60	$0.65	$1.11	1.9%

On a $20 item running a 15% net margin, the top standard band removes more than a third of the profit on every unit sold in the gap — and it lands precisely when the product is selling well, because that is what drives days of supply down.

05The exemptions

Check these before you restructure anything. Per Amazon’s fee page and the 2026 update:

• New-to-FBA sellers: no fee for the first 365 days after your first inventory arrives.
• New parent ASINs: no fee for the first 180 days after the ASIN’s first unit is received.
• Low-volume products: no fee if the FNSKU shipped fewer than 20 units in the trailing 7 days.
• AWD auto-replenishment: FNSKUs replenished into FBA from Amazon Warehousing and Distribution are eligible for a waiver. Amazon applies an auto-replenishment ratio test; seller-tool guides put the ratio at 70% or more of inbound units coming via AWD. Confirm the current ratio on the AWD program page before relying on it.
• Grocery: exempt.

There is no seasonal exemption. Q4 sell-through that drains a SKU is charged like any other.

06The reorder trigger that survives this

Your instinct will be to hold more stock. Resist it: it walks straight into the aged-inventory surcharge at day 181 and the storage utilization surcharge above 22 weeks of cover. The fee is a timing penalty, so the fix is a timing rule.

Your reorder point, in days of supply, is the whole replenishment gap plus the threshold:

reorder point (days) = 28
                     + supplier production time (actual recent performance, not the quote)
                     + transit time (ocean / air / ground)
                     + customs clearance (no longer a formality on low-value imports since the de minimis suspension)
                     + Amazon receiving and check-in (plan 5 to 14 days; longer in Q4)
                     + your own reaction time (PO approval, payment, booking)

Worked example, a standard-size SKU shipping 10 units a day: 28 + 25 production + 30 ocean + 4 customs + 10 receiving + 3 reaction = 100 days of supply at the moment you place the order, i.e. 1,000 units on hand. If that number frightens you, the alternatives are shorter lead times (air, domestic buffer stock) or holding the buffer outside FBA — in AWD, which also earns the waiver, or in a 3PL near a fulfillment center (the trade-off is worked through in AWD versus a 3PL for buffer stock) — and feeding FBA in smaller, more frequent lots. Both convert a fee problem into a logistics decision, which is the better kind of problem.

Model the cash side. The cash flow planner maps deposit, balance, freight, receiving and payout onto a timeline so you can see how long the buffer ties up money. Nothing is stored and nothing leaves your browser.

07Common mistakes

• Reading parent-level stock. Since January 2026 the fee is per FNSKU. A dashboard that only shows the parent is the wrong shape for this fee.
• Treating “in transit” as “in stock”. Units on a truck or in a fulfillment-center yard are not available inventory and do not count toward days of supply — which is one more reason the inbound placement split decision is a receiving-time decision, not just a fee decision.
• Reordering at 28 days. By the time the order arrives you have been under the line for the whole lead time and paid on every unit.
• Confusing this with the storage utilization surcharge. That one uses weeks of cover over 13 weeks and punishes excess; this one uses days of supply over 30 and 90 days and punishes shortage. The safe corridor between them is roughly 28 days to about 22 weeks of supply.

One check before you close this tab: open FBA Inventory, sort by historical days of supply, and count how many FNSKUs sit under 40. That number is your exposure for the next reorder cycle.

Frequently asked

What is the low-inventory-level fee threshold?

28 historical days of supply. Amazon assesses the metric over the last 30 days and the last 90 days and charges the fee only when both are below 28. If either window is 28 or above, the fee does not apply.

Am I charged for being out of stock?

No. The fee is charged per unit shipped while the FNSKU is below the threshold. A product with zero sales incurs nothing; a product selling briskly while thin is charged on every order.

Does one low variant affect the whole listing?

Not since January 15, 2026. The metric is now calculated per seller-FNSKU, so only the thin variant's own units are charged. Before 2026 it was assessed at parent-ASIN level.

Where do I see my historical days of supply?

Seller Central, Inventory, FBA Inventory: the table has a Historical days of supply column you can sort and filter. The Fee Preview report under Reports, Fulfillment shows the estimated fee per FNSKU.

Does Amazon Warehousing and Distribution avoid it?

FNSKUs auto-replenished from AWD are eligible for a waiver, subject to an auto-replenishment ratio that Amazon publishes on the AWD program page. Holding buffer stock in AWD and feeding FBA from it is the main structural way round the fee.

Is the fee avoidable by switching to merchant fulfillment?

Yes, in that it is an FBA charge. Whether the trade is worth making depends on your own fulfillment cost — run both through the margin calculator.

Sources

1. Update to U.S. Referral and Fulfillment by Amazon fees for 2026 (average +$0.08 per unit; no new fee types; effective January 15, 2026), Amazon Selling Partner Services Primary source accessed 2026-09-04
2. 2026 US Referral and FBA fee changes summary (low-inventory-level fee at seller-FNSKU level; bulky products in scope), Amazon Seller Central Help Primary source accessed 2026-09-04
3. Low-inventory-level fee further explained (28-day threshold on both 30-day and 90-day windows; AWD auto-replenishment waiver), Amazon Seller Forums, official announcement Primary source accessed 2026-09-04
4. Amazon low-inventory-level fee explained: 2026 rates and exemptions ($0.32–$1.11 standard, ~$2.09 bulky; 365-day, 180-day and 20-unit exemptions), PrepVia Secondary accessed 2026-09-04
5. 2026 Amazon FBA fee changes: full rate card (FNSKU-level calculation; grocery exemption; bulky tiers added), Goat Consulting Secondary accessed 2026-09-04