Marketplace fees are step functions: 5 prices where a higher price pays you less

SU — Wed, 04 Nov 2026 10:20:41 +0000

Marketplace fee schedules look like smooth percentages. They are not. They are step functions, and a step function has a property that breaks the usual pricing instinct: raising the input can lower the output.

I work on SellerUtility, a tool for Amazon and Walmart sellers, and we wanted to know how often that happens. So we did the boring thing: run a fee engine over every cent from $3.00 to $60.00 and look for places where one more cent of price pays the seller less.

The sweep

Net payout per unit is price - referral fee - fulfillment fee. The idea fits in a few lines (a sketch of the approach, not our production code):

def find_cliffs(net, lo=300, hi=6000):
    # net(price_in_cents) -> payout in cents for one fixed category/box
    return [p for p in range(lo + 1, hi + 1) if net(p) < net(p - 1)]

We ran that shape of check across 499 scenarios (every fee category, four packed-unit boxes per marketplace) on Amazon's 2026 FBA cards and Walmart's current fee schedules. The result was 646 cliffs. The surprising part is where they sit.

646 cliffs, 5 prices

Every cliff falls on one of five prices: $10.00, $10.01, $15.01, $20.01 and $50.01. That is a consequence of how the schedules are built: fulfillment fees change band at fixed price thresholds, and some referral rates step up on the whole price once you cross a line.

A few concrete cases from the data (2026 non-peak card, rate-card arithmetic):

A small standard, 4 oz FBA item nets $0.95 less at $10.00 than at $9.99, in all 36 fee categories.
In Beauty, Health and Personal Care the same item keeps $6.61 at $9.99, $5.66 at $10.00 and $4.97 at $10.01. It does not pay as much as $9.99 again until $11.94, so everything from $10.00 to $11.93 is a dead zone.
The deepest cliff we found is -$1.39 at $20.01 in Clothing and Accessories, where the referral rate goes from 10% to 17% of the whole price.
Walmart inverts one of them. A 0.5 lb Beauty item on WFS nets $4.74 at $9.99 and $5.75 at $10.00, because the $1.00 WFS surcharge applies only below $10. There, $10.00 is a jump up.

The full write-up, with a chart per category and a CSV, is in Amazon and Walmart fee cliffs 2026.

What this means if you write pricing code

Never assume monotonic payout. If your repricer or margin model treats "higher price, higher profit" as true, it will happily walk into a dead zone. Test it with a property check like the one above.
Evaluate fees at the candidate price, not the current one. A fee computed once at today's price and reused is wrong the moment the candidate lands on the other side of a threshold.
Version the rate card. Amazon's peak card (October 15 onward) changes the numbers, so a cliff table without a card date is not reproducible.
Mind the boundary operator. "Under $10" and "$10 or less" are different thresholds, and different fee lines can use different ones. See the Walmart WFS surcharge under $10 breakdown for how that plays out.

If you just want to check a specific product rather than read about it, the Amazon FBA fee calculator shows the payout at a given price, and the Amazon FBA fees 2026 and Walmart seller fees 2026 guides cover the schedules themselves.

Caveats

These are numbers from the published rate cards, not from a live seller account. Fees change, so check the current card before relying on any single figure. The sweep also does not cover every cost a seller pays, such as storage, returns or advertising.

Curious whether other people have hit this in their own pricing code: did you model fees as a step function from the start, or find out the hard way?

DEV Community: SU

Marketplace fees are step functions: 5 prices where a higher price pays you less

The sweep

646 cliffs, 5 prices

What this means if you write pricing code

Caveats