Your FBA fees changed and nobody told you
Amazon can re-measure a unit and move it into a heavier fee tier without any notification you would notice. Here is how to catch it before it eats a quarter of margin.
September 14, 2026 · 6 min read
A fee change almost never announces itself. There is no red banner in Seller Central saying "this SKU now costs you more to ship". What happens instead is quieter: a unit gets re-measured in a fulfillment center, the recorded dimensions or weight shift slightly, the SKU crosses a size-tier boundary, and every order from that moment forward is charged at the higher rate.
The seller finds out weeks later, usually by noticing that a product that used to feel profitable now feels tight, and blaming advertising.
Why the small changes are the expensive ones
Size tiers are cliffs, not slopes. A fraction of an inch or a few grams can be the difference between two tiers, and the fee difference across a tier boundary is not proportional to the physical difference. That is what makes this failure mode so unfair: the smallest measurement error produces the largest cost jump.
Then it compounds. The referral fee is a percentage, so it scales with price. The fulfillment fee is flat per unit, so it scales with volume. Your best-selling SKU is therefore the one where a single tier change does the most damage, and it is also the one you are least likely to re-audit, because it is working.
What to actually check
Four checks catch most of it:
- Compare the dimensions and weight Amazon has recorded against the ones you measured. Amazon charges on its own numbers, not yours.
- Pull the fee breakdown per unit and per order, not the monthly total. Averages hide tier changes.
- Watch for the fee types that are easy to forget: storage, aged inventory surcharges, returns processing, and removal.
- Recheck after any packaging change, and after any new shipment of an existing SKU.
Dispute the measurement, not the fee
If Amazon's recorded dimensions are wrong, the fee is not the problem — the measurement is. Requesting a re-measure and providing your own documented dimensions is the fix, and it applies going forward, so the sooner you catch it the less it costs.
MySellerHQ reads your fee data straight from Amazon's Selling Partner API with read-only permissions and shows you the per-SKU picture, so a tier change shows up as a change instead of as a slow bleed you notice next quarter.