Your December storage bill is calculated from what you held in November, and the low-inventory fee on the units you shipped in November was decided by what you held in August. By the time either number shows up, the decision that caused it is a season old.
Most FBA fee guides treat storage as one line and the low-inventory fee as a separate topic. They are one topic. Amazon built a fee for holding too little and a set of fees for holding too much, and the only way to avoid both is to know exactly where each one starts. That is what this post is for: the mechanism and the thresholds of all four charges, laid side by side so the corridor between them is visible.
Amazon changed several of these rates during 2026 and third-party sources now quote different figures for the same fee. Section 6 shows the disagreements. Thresholds (28 days, 22 weeks, 181 days) are consistent across Amazon's own statements and are what this post is built on. Where a dollar figure appears it is labeled as a published range. Pull the exact rate for your size tier from Seller Central before you model anything. Evolve Media Agency does not sell inventory management or fulfillment services; we sell creative and listing work, and this post exists because storage fees are the cost our clients most often misjudge.
For the full fee stack (referral, fulfillment, the April 2026 fuel surcharge, inbound placement) the FBA fee breakdown is the reference. This post goes deep on the four charges that depend on how much you hold and for how long.
Two Fees Pulling In Opposite Directions
Before Amazon introduced the low-inventory-level fee in April 2024, the incentive was simple: hold as little as you can get away with, because every cubic foot costs money every month. Since then, holding too little costs money too, per unit shipped, on every order while you are under the threshold. The two fees are designed to push sellers into a band that is convenient for Amazon's network, and the band is narrower than most brands run.
| Charge | What Triggers It | Charged On | Pushes You To |
|---|---|---|---|
| Monthly storage fee | Any inventory in an FC | Cubic feet held, daily average, monthly | Hold less |
| Aged-inventory surcharge | A unit reaches 181 days in an FC | Cubic feet of aged units, monthly, escalating | Turn faster |
| Storage utilization surcharge | Account-wide stored volume divided by shipped volume exceeds 22 weeks | All cubic feet held, added to monthly rate | Hold less relative to sales |
| Low-inventory-level fee | Historical days of supply below 28 on both the 30-day and 90-day measure | Each unit shipped while under threshold | Hold more |
Read the last column top to bottom. Three fees say hold less. One says hold more. The seller's job is to find the amount of stock that satisfies all four at once, per SKU, and to keep it there while sales velocity moves. The rest of this post takes each meter in turn and then builds the corridor.
Meter One: Monthly Storage
The monthly storage fee is the simplest of the four and the one most sellers already model. Amazon measures the daily average volume of your inventory in cubic feet, by size tier (standard versus oversize), and bills it monthly at a per-cubic-foot rate. The rate has two seasons: January through September, and October through December, when it is roughly three times higher.
Cubic feet, as Amazon measures them. Amazon uses the packaged dimensions of the unit as measured at receipt, rounded up, including any Amazon-applied packaging. A product you think of as 0.4 cubic feet is often billed at 0.5 or more. The FBA Inventory report shows the measured volume per FNSKU; use that figure in every model rather than your supplier's spec sheet.
Two things make this fee larger than the rate card suggests. First, the volume is a daily average, so a big inbound that lands on the first of the month is billed for the whole month, while the same inbound landing on the 28th is barely billed. Timing inbounds to the end of a month is a real, boring, repeatable saving. Second, the fee is charged on everything, including units that are reserved, in transfer between FCs, or unfulfillable. Stranded and unfulfillable inventory costs the same to store as sellable stock and earns nothing.
Published 2026 standard-size off-peak rates cluster around $0.78 to $0.99 per cubic foot, with October through December around $2.25 to $2.40. Oversize rates are lower per cubic foot and the units are larger, which usually makes oversize storage the bigger dollar line. Section 6 explains why those are ranges.
Meter Two: The Aged-Inventory Surcharge
This is the fee that used to be called long-term storage and used to start at 365 days, then 271, and now starts at 181 days. It is charged monthly, per cubic foot, on any unit that has been in Amazon's network for 181 days or more, and it escalates in 30-day bands. Past a year the surcharge is several times the base monthly rate, and Amazon applies a per-unit minimum for small items so a tiny unit cannot age cheaply.
The mechanism that matters more than any rate: Amazon ages inventory first in, first out at the FNSKU level. A unit that arrived 200 days ago is aged even if you sent 500 fresh units last week, and the fee is charged on the old unit's volume regardless of how many new ones you added. Sending more stock does not reset the clock on the stock already there. Only shipping it, removing it or disposing of it does.
| Inventory Age | What Happens | Published 2026 Surcharge, Range Across Sources |
|---|---|---|
| 0 to 180 days | Monthly storage fee only | None |
| 181 to 270 days | Surcharge begins, three 30-day bands | Roughly $0.50 to $1.50 per cubic foot per month, rising by band |
| 271 to 365 days | Steep step up | Sources range from about $1.65 to $5.90 per cubic foot; see section 6 |
| 366 days and beyond | Highest tiers, with a per-unit minimum | About $6.90 to $7.90 per cubic foot, or a per-unit minimum, whichever is greater |
The direction is undisputed and it is the only thing you need to plan against: a unit that reaches day 181 starts costing you extra every month, and a unit that reaches day 271 costs a lot extra. Amazon runs the inventory age snapshot on the 15th of each month, so a unit that turns 181 days old on the 16th is billed from the following month. The practical trigger for action is 120 days, because a removal order takes time to process and you want the unit gone before the snapshot, not after.
Meter Three: The Storage Utilization Surcharge
This is the fee most often confused with the aged surcharge, and it works differently. It is account-wide, it does not care how old any individual unit is, and it is added to your base monthly storage rate on every cubic foot you hold.
Storage utilization ratio. Your average daily inventory volume over the trailing 13 weeks, divided by your average daily shipped volume over the same period, expressed in weeks. If you hold 30 cubic feet on average and ship 1 cubic foot a day, your ratio is 30 days, or about 4.3 weeks. When the ratio exceeds 22 weeks, Amazon adds a surcharge to the monthly storage rate, in tiers that rise with the ratio. Professional sellers only; new sellers are typically exempt for a period.
Because it is account-wide, one slow SKU with a lot of volume can push the whole account over 22 weeks and raise the storage rate on your best sellers. That is the trap. A brand with nine fast movers and one dead oversize SKU can be paying a surcharge on all ten because of the one. The SKU rationalization guide is the right tool for that case: the dead SKU is costing more than its own storage line shows.
The 22-week threshold is the upper wall of the corridor. It is not a per-SKU number, so the planning target has to be set per SKU at something well under 22 weeks so the blended account ratio stays clear of it with room for a slow month.
Meter Four: The Low-Inventory-Level Fee
Introduced April 2024, this is the one that pulls the other way. It is a per-unit fee added to the fulfillment fee on every unit shipped while a product's historical days of supply is below 28 days.
The mechanism, from Amazon's own explanation in its seller forums: historical days of supply is calculated at the parent-product level as average daily sellable inventory divided by average daily units shipped. Amazon computes it over two windows, the last 30 days and the last 90 days. The fee applies only when both windows are below 28 days. If either is at 28 or above, no fee. That dual-window rule is the escape hatch: a short-term inbound that lifts the 30-day figure above 28 stops the fee even while the 90-day figure is still low.
Three details that bite. Inbound inventory does not count, so a shipment stuck in receiving does nothing for the calculation until it is checked in. Reserved units do not count as sellable. And the fee is tiered by how far under 28 days you are: the published 2026 ranges run from about $0.32 per unit at 21 to 28 days of supply up to about $1.11 for standard-size units under 14 days, with bulky tiers reported as high as about $2.09 after Amazon expanded the fee to small and large bulky products in January 2026. Two sources also report the measurement moved from parent-ASIN to FNSKU level in January 2026; Amazon's older forum explanation says parent level. Check the Historical Days of Supply column in FBA Inventory, which shows you what Amazon is actually using.
The fee shows up as a line inside the FBA fulfillment fee on each order, which is why sellers miss it. On a SKU shipping 300 units a month that dips under 14 days of supply for a month, that is $300 or so of fees for the privilege of running out of stock.
Why The Published Rates Disagree
We checked eight 2026 guides to these fees while writing this. They agree on the thresholds and disagree on almost every dollar figure.
| Figure | Values Quoted Across 2026 Sources | What Is Going On |
|---|---|---|
| Standard off-peak storage | $0.78, $0.87, $0.99 per cubic foot | Amazon appears to have revised the rate mid-2026; some guides carry the January figure, some the July one, one may be quoting a utilization tier |
| Q4 standard storage | $2.25 or $2.40 per cubic foot | Same revision; two sources say it was reduced, one says raised |
| Aged surcharge, 181-270 days | $0.50-1.50 by band; $1.25 flat; $1.50 flat; $3.80-4.20 by band | At least one guide is mixing the surcharge with total storage cost; at least one is out of date |
| Aged surcharge, 365+ days | $6.90 or $7.90 per cubic foot | A new 15-month tier was reported in January 2026; guides that predate it stop at $6.90 |
| Low-inventory threshold | 28 days; one source says 35 days for some SKUs in 2026 | Amazon's own statements say 28; the 35 may be a planning recommendation reported as a rule |
The pattern is worth naming: every one of these sources sells inventory software, prep, warehousing or seller tools, and every one has an incentive to publish a confident number that ranks. None of them link to a dated Amazon rate card for the figure they quote. The technical descriptions of how the fees work are consistent and reliable. The rates are not, and a stale rate in a landed-cost model is worse than no rate.
So this post does not pick one. Open Seller Central, go to the FBA fee schedule under Pricing, and read the current storage and surcharge tables for your size tier. Then run the Fee Preview report for your actual FNSKUs, which applies the current rates to your measured volumes. That report is the only source that will agree with your next invoice.
The Corridor: 28 Days To 22 Weeks
Put the four meters on one axis and the planning target appears.
Why 35 rather than 28 as the floor: the fee is decided on trailing averages and inbound does not count, so if you reorder at 28 you will be under 28 by the time the stock is sellable. A week of buffer covers receiving delays. Why 60 rather than 154 as the ceiling: storage cost per unit sold rises with every day of supply, Q4 triples it, and a SKU sitting at 120 days of supply in September is a SKU whose oldest units will hit 181 days in December at peak rates. The 22-week wall is an account-level backstop; the per-SKU target sits well below it.
The aged clock is the one that breaks the corridor model, because it runs on individual units rather than on days of supply. A SKU at a healthy 45 days of supply can still have a tail of units from an oversized order eight months ago. Days of supply says you are fine; the inventory age report says you are paying. Both reports have to be read, and the reorder point guide covers how to set order quantities so the tail never forms.
A Worked Example: One SKU, One Year
A standard-size unit measured at 0.25 cubic feet, selling 10 units a day. Three ordering strategies, twelve months, storage-related fees only. Rates are illustrative and rounded to the middle of the published ranges; the point is the shape.
Strategy A looks cheapest on the storage line and costs nearly twice strategy B once the low-inventory fee is counted, plus the stockouts it does not show. Strategy C saves on reorders and freight and pays for it five times over in storage and aging. Strategy B is the corridor. The exact dollars will differ with your rates; the ranking will not.
The number that should go in your unit economics is the last row: storage-side cost per unit sold. On strategy B it is about the same as a referral fee on a $2.50 item, small enough to ignore. On strategy C it is a real line. The true cost of an Amazon sale shows where that line sits against everything else.
The Q4 Squeeze
October through December is when all four meters run against you at once. Storage triples. Sales spike, which drops days of supply, which triggers the low-inventory fee on your best sellers at the worst time. Capacity limits tighten, so you cannot simply send more. And any slow SKU whose units were young in the summer crosses 181 days in the peak-rate months.
A SKU at 45 days of supply in September can be at 20 days in November on the same units, because the denominator doubled. Plan Q4 days of supply against Q4 velocity, not September's.
Sending the whole Q4 order in September to beat capacity limits means paying triple storage on units that will not sell until December. Stagger inbounds to arrive late in each month.
Units received in June are 181 days old in December. An aged surcharge on top of Q4 base rates is the most expensive cubic foot on Amazon. Pull the inventory age report in August and act.
The 13-week trailing ratio still remembers August's slow shipping when you inbound for Q4. Big September inbounds can push the account over 22 weeks before Q4 sales pull it back.
The calendar side of this, cutoffs and the week-by-week September checklist, is in the Q4 inventory planning guide. This post is the math underneath it.
Exemptions And Edge Cases
Amazon carves out several exemptions, mostly to the low-inventory fee. These are as reported at the fee's launch and in 2026 coverage; confirm the current list in Seller Central because Amazon adjusts them.
- New sellers were exempt from the low-inventory fee for their first 365 days at launch, and new-to-FBA products for their first 180 days. Multiple 2026 sources still describe these exemptions.
- Low-velocity products, reported as under 20 units shipped in a week, are exempt from the low-inventory fee, because 28 days of supply on a product that sells two units a week is not a meaningful target.
- Products auto-replenished through Amazon Warehousing and Distribution are exempt from the low-inventory fee, since Amazon controls the FBA stock level. This is the single strongest argument for AWD on high-velocity SKUs, and the AWD vs FBA guide weighs it against AWD's own costs.
- Grocery is reported as exempt from the low-inventory fee after the January 2026 changes.
- Out of stock means no units shipped, so no low-inventory fee. It also means no sales, so this is an exemption in name only.
- The aged surcharge has category exclusions in its lower bands (apparel, shoes and some others were excluded from the 181-270 day tiers in earlier versions), and the storage utilization surcharge applies to Professional accounts, with new sellers typically exempt for a period.
Seller Central's FBA Inventory page shows an exemption flag per product. If the flag says exempt, the fee is not being charged regardless of days of supply. If it says the fee will be applied, the number next to it is Amazon's calculation and it is the one to fix.
The Ecom Profit Box
Our library of ecommerce growth guides, including the unit economics and inventory frameworks behind this post.
Get It FreeFind Out What Storage Is Really Costing
Bring your FBA Inventory and inventory age exports. We will show you which SKUs are outside the corridor and what each one costs per unit sold.
Book A CallPlanning Every SKU To Stay Inside
A monthly routine that takes about an hour for a catalog of 50 SKUs.
Step 7 is where most brands go wrong, because it fights the instinct to order big and save on freight per unit. Freight savings are visible on the invoice; the storage and aging costs of the extra units are spread across six months of statements and never attributed to the order that caused them. Run the per-unit-sold figure from step 6 against the freight saving before every large PO. The multi-channel forecasting guide covers the demand side of step 7 when the same SKU also sells on Shopify or TikTok Shop.
When To Move Stock Out Of FBA Entirely
Some inventory should never sit in an Amazon fulfillment center longer than a few weeks, and the four meters tell you which.
Slow oversize SKUs
Low per-cubic-foot rates and large volumes make oversize the biggest storage line on most accounts, and a slow oversize SKU is also the usual cause of a utilization surcharge. A 3PL at a fraction of the rate, shipping into FBA in small replenishments, is often cheaper even after the extra handling. The 3PL vs FBA framework runs that comparison.
Deep seasonal stock
Inventory that sells in one quarter and sits for three should not be aging in FBA. Hold it upstream and inbound in the corridor. AWD exists for exactly this, with the low-inventory exemption as a bonus.
Anything past 120 days with no plan
A removal order to your own warehouse or a 3PL costs a fee per unit and stops the aging clock. Against a 271-day surcharge at Q4 rates, it usually pays back inside two months. The alternative, a discount deep enough to move it, is often cheaper still and the 13-week cash flow model will show you which.
Three of Amazon's storage fees say hold less. One says hold more. The corridor between them is about 28 days to 22 weeks of supply, and the only thing in there is the money you keep.
One last honest note. Nothing in this post makes the fees smaller; Amazon sets them and revises them without asking. What it does is make them predictable, which is what a fee has to be before you can price around it.
What To Remember
- Amazon charges for holding too little (low-inventory fee) and too much (storage, aged and utilization surcharges); the planning corridor between them is about 28 days to 22 weeks of supply.
- The low-inventory fee applies per unit shipped only when both the 30-day and 90-day historical days of supply are under 28, and inbound units do not count until received.
- The aged surcharge starts at 181 days per unit, first in first out, and sending fresh stock does not reset the clock on old units; act at 120 days.
- The storage utilization surcharge is account-wide above 22 weeks, so one dead oversize SKU can raise the storage rate on every SKU you sell.
- Published 2026 dollar rates disagree across sources because Amazon revised them mid-year; read thresholds here and rates from your own Seller Central rate card and Fee Preview report.
- Target 35 to 60 days of supply per SKU and time inbounds for month-end, since storage is billed on a daily average.
- Q4 runs all four meters at once: rates triple, velocity drops days of supply, and summer inventory crosses 181 days in December.
Where This Came From
- Amazon Seller Central, FBA fee schedule and the monthly storage, aged-inventory surcharge, storage utilization surcharge and low-inventory-level fee help pages (login required; not linked). These are the authoritative rate cards and the reason this post prints thresholds rather than dollar figures.
- Amazon Seller Forums, "Low-inventory-level fee further explained", Amazon staff explanation of the dual 30-day and 90-day window, parent-level calculation and the inbound-does-not-count rule.
- Webgility, low-inventory fee guide; AMZ Prep, January 2026 changes including the bulky expansion and reported FNSKU-level measurement. Both sell inventory or prep services.
- Seller Essentials, aged-inventory surcharge guide, and Warehousing Costs, FBA storage fees guide, two of the eight 2026 sources compared in section 6. Both sell related services.
- Inference note: the corridor (35-60 days per SKU, action at 120 days of age) and the worked example in section 8 are our planning recommendations derived from Amazon's thresholds, not Amazon guidance. The dollar figures in section 8 are illustrative mid-range values and will not match any specific rate card.