Amazon Fee Increase: What Three Fee Changes Did to Our Margin

✨ Written with AI assistance from our own settlement data, and reviewed by Avanta Global EOOD before publication. Learn more

Short answer: a fee increase does not show up in your margin as a percentage. It shows up as a lower break-even ACoS, and nothing in the ads console tells you it moved. On our own Amazon Australia listing, one fee change cost A$2.28 per unit and seven points of break-even ACoS. A second "gap" between Amazon's fee estimate and what we were charged turned out to be GST. A third, a package size left over from our previous supplier, has been worth little per sale and about a third of our storage bill.

The three fee effects we measured

We sell one product on Amazon.com.au: a bubble mailer bundle, Office Products, fulfilled by Amazon, product cost A$7.40 per unit. Every figure comes from our settlement line items and Amazon's fee-estimate API for that SKU.

Fee effect	What changed	Per unit	Per year at our pace*
Referral fee, 14–16 July	about 5.6% → 13.0% of the price paid	+A$2.28 (A$1.97 → A$4.25)	about A$4,900
FBA fee: estimate vs charge	Estimate A$9.86, charged A$10.85 on every unit	A$0.99 (exactly the 10% GST)	about A$2,100
Package size on record	Old supplier's pack (10.3 L) vs our current pack (6.86 L)	about A$0.05 on the FBA fee	storage: about a third of the monthly charge

*Pace: 439 units in the 75 days from 16 July to 28 September, 5.85 units a day. The yearly column multiplies the per-unit change by that pace; it is arithmetic, not a forecast.

1. The referral fee: a change that arrived silently

Our referral fee moved to the published 13% Office Products rate in mid-July, with no notice in our workflow. We covered it in detail in our referral fee change post. Here is what it did to the margin, at our list price of A$34.99:

	Old referral (~5.6%)	13% referral
Referral fee	A$1.96	A$4.55
FBA fee	A$10.85	A$10.85
Product cost	A$7.40	A$7.40
Contribution before ads	A$14.78	A$12.19
Break-even ACoS	42.2%	34.8%

Break-even ACoS is contribution divided by price. The ads did not change. The bar they are judged against dropped by 7.4 points, and every campaign that sat between 35% and 42% ACoS went from profitable to loss-making on the same day. We explain how to read that bar in ACoS vs profit.

2. The FBA fee: an estimate is not a fee

Amazon's fee-estimate API, queried on 30 September at A$34.99, returns a fulfilment fee of A$9.86. The settlement charged A$10.85 on every one of our 543 units from 27 May to 28 September, the same amount every week. If we had priced from the estimate, our break-even ACoS would have read 37.7% instead of 34.8%: three points of headroom that did not exist.

The difference is GST. Amazon's Australian pricing page lists fees excluding GST, and A$9.86 is the published fee for a parcel of 2,001–3,000 g. A$9.86 plus 10% is A$10.846, which is what we pay. Our storage lines make it visible: each month the settlement shows a Base fee and a separate Tax on fee at exactly 10.0%. The fulfilment fee arrives as one line with the tax already inside it.

The estimate got the referral fee right (A$4.55, 13% of A$34.99). It was only the fulfilment fee where estimate and charge parted.

3. The package size: a number filled in once keeps charging

Amazon charges the FBA fee by the larger of real weight and volumetric weight (length × width × height in cm ÷ 4,000, per the pricing page). Our pack weighs 0.4 kg. The size Amazon holds for it is 30.9 × 23.0 × 14.5 cm, which is 10.3 litres and a volumetric weight of 2.58 kg. The fee comes entirely from the box.

That size belongs to the pack our previous supplier used. Our current supplier's pack measures 24 × 13 × 22 cm, 6.86 litres. We found the mismatch on 14 September by comparing Amazon's record with the supplier's carton, corrected the dimensions on the listing on 15 September, and opened a re-measure and refund case.

What has changed since: nothing yet. On 30 September Amazon's catalog still held 30.9 × 23.0 × 14.5 cm, its inventory report still counted 0.010305 m³ per unit, the fee estimate was still A$9.86, and the settlement charged A$10.85 on every unit through 28 September. Storage for September has not been charged yet.

What it is worth, once corrected:

• FBA fee: 6.86 litres is 1.72 kg volumetric, the 1,501–2,000 g band at A$9.81. That is 5 cents a unit before GST. The published bands are nearly flat here.
• Storage: Amazon charges storage per cubic metre (A$37.00 January–September, A$51.80 October–December). A pack a third smaller should cost a third less to store. Our storage charge posted on 6 September was A$259.02 including GST; a third of that is about A$86 for one month, and the rate rises 40% from October.

What we got wrong

On 3 August we opened a case claiming Amazon was overcharging our fulfilment fee by A$0.99 a unit, using exactly the estimate-vs-charge gap above. Amazon re-measured the pack, found 30.91 × 23.01 × 14.5 cm and 0.4 kg, and declined the next day. They were right: the gap was GST, and our own notes already said the estimate excludes it. Six weeks later we logged the same gap as unexplained again.

That case also measured the right box at the wrong time: the old supplier's pack. When the smaller pack arrived, the record stayed, and no report flagged it, because Amazon's catalog, fee estimate and storage report all agreed. They were reading the same old number. It took a measurement from outside Amazon, the supplier's carton, to show it was wrong.

How to check your own account

1. Compare the estimate with the charge. Take the fulfilment fee from Amazon's fee preview for your SKU, then the FBAPerUnitFulfillmentFee line per unit from your settlement. A gap of exactly your tax rate is tax; anything else deserves a closer look. Our settlement report guide shows which lines to use.
2. Track fees per unit by week. A step in the referral or FBA fee per unit is a fee change. Its date tells you which prices and ad targets it made stale.
3. Check the package size Amazon holds against a real measurement, especially after changing supplier or packaging. Divide the volume in cm³ by your marketplace's divisor and see which weight band you land in.
4. Recompute break-even ACoS after every fee change. The break-even ACoS calculator does it in your browser; the settlement profit reader reads fees straight from a report.

AgentXray runs the same checks continuously from your settlement data.

FAQ

Why is my Amazon FBA fee higher than the fee estimate? On our Australian account the whole difference was 10% GST: the estimate excludes it, the settlement charges it. Check whether the gap equals your tax rate before opening a case.

Does a smaller package lower the FBA fee? Only if it moves you into a lower weight band. For us the saving was 5 cents a unit; the larger effect was on storage, which is charged by volume.

How much does a fee increase cost in ad headroom? Exactly the fee change divided by your price. At A$34.99 our referral fee rose A$2.59 a unit (A$1.96 → A$4.55), and 2.59 ÷ 34.99 is the 7.4 points our break-even ACoS lost. Across what buyers actually paid, including discounts, the rise averaged A$2.28.

About this article

Figures come from Avanta Global EOOD's own Amazon.com.au data for one SKU: settlement line items 27 May – 28 September 2026 (543 units), Amazon's fee-estimate API, catalog record and inventory report read on 27–30 September, and a product cost of A$7.40 per unit. Published fees and the volumetric divisor are quoted from Amazon's Australian pricing page, read on 30 September 2026. Currency is Australian dollars. Measured on 30 September 2026. The re-measure case was still open on that date. We are not accountants; check your own settlement before acting on a fee.