Amazon Low-Inventory-Level Fee 2026: The Per-FNSKU Rule Most Sellers Still Miss

Last updated: 2026-10-03

Direct answer: Amazon's low-inventory-level fee is charged per shipped unit, on top of the FBA fulfillment fee, when a product's historical days of supply drops below 28 days. Since January 15, 2026 Amazon measures days of supply per FNSKU — every child variation is scored on its own instead of being averaged into the parent ASIN. The fee fires only when both the trailing 30-day and the trailing 90-day windows sit below 28 days, and the rate band is taken from the higher of the two windows. Rates run $0.32–$2.09 per unit depending on size tier.

What actually changed on January 15, 2026

The rate card is not the story — the unit of measurement is. Before 2026-01-15 days of supply was effectively assessed at the parent ASIN level, so a healthy average could mask a variation that was chronically thin. From that date Amazon scores each FNSKU separately, refreshes the figure weekly, and bills any child that falls short. For catalogues with many variations — apparel sizes and colours above all — this moved a fee that almost never appeared onto individual children that were always thin.

The metric itself is unchanged: average daily inventory units on hand ÷ average daily shipped units, computed over the trailing 30-day and trailing 90-day windows.

The trigger: both windows, not either

This is the part most calculators get wrong. The fee is charged only when both windows are below 28 days. One window at 28 or above switches the fee off entirely. And the rate band comes from the greater of the two windows — which is counter-intuitive, because a higher days-of-supply figure lands in a cheaper band.

Worked example, Large Standard (up to 3 lb): 30-day window = 12 days, 90-day window = 25 days. Both are under 28, so the fee fires. The band comes from the higher window (25 days → the 21–28 day band) at $0.36 per unit, not the 12-day figure. Being briefly thin does not automatically mean the deepest band.

One more edge case that saves real money: a window with zero shipped units leaves days of supply undefined, and Amazon treats that as above 28 — so no fee. Do not model a dead window as "0 days of supply" and assume the worst band.

2026 rate card (per shipped unit)

Scope: standard-size and Small/Large Bulky products. Extra-Large tiers sit outside this fee — nothing is charged there. Verified 2026-09-15 against Seller Central help page GV43F6S76Y9DHYRH.

Why variation-heavy catalogues get hit hardest

Take a six-variation apparel parent averaging 41 days of cover. Under parent-level averaging, no fee. Scored per FNSKU, the black / size L child sits at 11 days on both windows — it bills $0.89 per shipped unit (Small standard, under 14 days). At 300 units a month that child alone adds $267/month, while the parent dashboard still looks healthy.

This is the structural reason apparel sellers felt the 2026 change most: a size curve is never uniform, and the tail of the curve is exactly what per-FNSKU scoring exposes.

How to switch the fee off

• You only need one window at 28 days or more to stop the charge — you do not have to fix both.
• The 30-day window responds first to a restock, so it is usually the fastest lever.
• Audit at child level, not parent level. Sort the FNSKU list by days of supply ascending and work the tail.
• Merge or retire chronically thin variations — a child that sells two units a month will keep re-triggering.
• Re-check weekly: Amazon refreshes days of supply on a weekly cycle, so a restock is not reflected instantly.
• Watch the 90-day window after a demand step-up — it lags the 30-day window and can quietly pull a child back under 28.
• Model the exposure before you commit: our inventory planner flags each SKU's forward days of supply against the same rate card.

Common modelling mistakes

• Averaging at parent level. Invalid since 2026-01-15 — the parent average no longer hides a thin child.
• Treating the fee as monthly. It is charged per unit shipped, on top of the FBA fulfillment fee.
• Modelling a zero-sales window as 0 days. Undefined days of supply reads as above 28, so nothing is charged.
• Using the 30-day window alone for the band. The band comes from the higher of the two windows.
• Pricing bulky SKUs off the standard range. Bulky runs $0.51–$2.09, not $0.32–$1.11.
• Applying it to Extra-Large. Those tiers are outside the fee.

The practical takeaway: the fee is small per unit but it lands on exactly the SKUs that are already weakest, and per-FNSKU scoring means it can no longer be averaged away. Score every child separately, and remember that lifting a single window to 28 days is enough to stop the charge.

Calculate your total FBA fees — including the per-FNSKU low-inventory fee — with our free calculator →