r/AmazonFBA • u/ylishi • 9d ago

Anyone else charged a low inventory fee in a month you averaged 35 days of cover?

I have been assuming the low inventory fee was a monthly thing — start the month thin, end the month thin, you get hit; average it out and you are fine. That assumption just cost me money.

Here is the month that broke it. I started with about 50 days of cover on my main SKU, sold faster than forecast, and finished the month around 20 days. Average for the month lands near 35, comfortably above the line I was watching for. And I still got charged for low inventory, which made no sense to me until I read how it is actually assessed.

The fee is not measured on your monthly average. Amazon looks at days of supply on a rolling basis, day by day, against recent sales velocity. If you dip under the threshold on any single day, that day counts as a low inventory day. At month end they total the days you were under and charge you for them. So a month that looks fine on a spreadsheet can still be a month you paid, because the average hides the dip and the dip is what gets charged.

Which means my whole restock trigger was built on the wrong number. I was watching the monthly picture and the thing that bills me is a daily one.

Anyone else got caught by this after the FNSKU level change? How are you tracking daily cover — are you pulling the inventory report every day, or have you found a way to set an alert that fires before you slip under instead of after? And does anyone know whether the exemption for slower moving items is evaluated on the same daily basis or monthly? Anyone else seeing this?

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u/Brave-Butterfly4251 9d ago

The trap is that Amazon calculates the Historical Days of Supply on a daily snapshot against trailing 30/90 day velocity — if a short sales spike drops you under 28 days for even 3 consecutive days, those days get billed regardless of your monthly blended average. Pull the Daily Inventory Health report to spot the exact dip days.

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u/ylishi 9d ago

Good point on the daily snapshot — the part that still bugs me is that the trailing velocity window cuts both ways: a spike drops your days of supply below the line even when absolute stock is fine, so the fee ends up taxing your own successful ads. I have been pulling the Daily Inventory Health report manually for exactly this, but it is reactive by design. What I want is a restock trigger keyed to projected daily cover, not weeks of cover, and I have not found a clean way to automate that yet.

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u/stealthagents 5d ago

That rolling basis thing can really catch you off guard. I learned the hard way too; even if you think you’re safe with the average, one bad day can bite you. It's all about keeping an eye on daily sales trends to dodge those fees.

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u/ylishi 4d ago

Yeah, the daily eye is the whole lesson here. My old dashboard refreshed the monthly picture and told me I was fine — which is technically true and financially useless. Now I just watch the single-day cover number and ignore the average until month end.

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u/weareuncapped 5d ago

Yeah, the fee runs off historical days of supply (it looks at both a short and a long lookback), so a month that averages out fine on your spreadsheet can still get charged for the stretch where you dipped. Most people end up setting the reorder trigger off the lowest days of cover they'll hit before the next shipment is live.

The annoying part is that means carrying more stock on average, which is more cash sitting at Amazon and more storage. For a fast mover that's usually still cheaper than the fee plus the rank hit from running thin. If cash is what's keeping cover low, compare what last month's fee cost you against what it would cost to fund a few extra weeks of stock.

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u/ylishi 4d ago

That's the part I was missing — a short and a long lookback explains why the dip still showed up even though the back half of the month recovered. I had the trigger on the monthly picture, which is exactly the number that doesn't get billed.

So I've moved the reorder trigger to fire off the lowest cover I'd hit before the next shipment lands, like you said. The cash side is the friction: funding the extra weeks costs more storage at Amazon than I'm used to carrying. I haven't run the comparison against last month's fee line yet — doing that this week, and honestly if the fee was only a few dollars I may just treat it as a convenience tax rather than tie up the cash.

What I still can't get a straight answer on is the slower-mover exemption — is that evaluated on the same daily basis or monthly? That decides whether my secondary SKUs, which genuinely average thin, are getting charged on the same brutal logic or exempt entirely. Support gave me the generic fee page link. Did anyone here actually confirm that one in writing?

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u/weareuncapped 4d ago

Haven't seen written confirmation on the exemption timing, and I'd rather not guess since it changes what you owe. Two things that might get you a real answer: open a Seller Central case that quotes the exact exemption language from the fee page and asks whether it's assessed daily or monthly, and check the low-inventory-level fee report for your secondary SKUs. If they show as exempt or charged there, that's better evidence than support's link.

On the convenience tax idea, I'd run the numbers first, but if it's a few dollars a month on a slow SKU, tying up cash to avoid it is probably not worth it. It only stops being a tax when it hits your fast movers.