Three months ago a partner showed me his case model for a 6,500-claimant mass arb. He'd built it carefully. Per-case fees were lined up at $125 for the AAA tier. Initiation fees were in. Arbitrator hourly assumptions were conservative.
He was off by $187,000.
Not because the math was wrong. Because the schedule isn't a linear function of headcount, and the model treated it like one.
This is the most expensive miss I see in plaintiff-side mass arb modeling. And it's almost always the same three errors.
Error 1: Per-case fees don't drop, they tier
AAA's consumer mass arb per-case fees go like this.
First 500 cases: $125 each, claimant side. $325 each, business side.
Cases 501 through 1,500: $75 each, claimant side. $200 each, business side.
After 1,500: $50 each, claimant side. $100 each, business side.
If you model a 6,500-claimant matter at $50 per case across the board, you're at $325,000 in claimant-side per-case fees. The real number is $337,500 ($125 × 500 + $75 × 1,000 + $50 × 5,000).
Twelve thousand five hundred dollars off the top, and that's the small version of the problem.
The bigger version is what happens when a Process Arbitrator knocks out cases in the first 500. You don't get refunded to a lower tier. You still paid $125 for that case. The defense doesn't have to win the challenge. It just has to slow it past the point where you've already paid the first-tier rate.
Error 2: The Final Fee is a separate line item that the defense can game
The Final Fee under AAA's Mass Arbitration Supplementary Rules is $600 per case in consumer matters, $750 in employment. Paid by the business. Important for the defendant's exposure model, irrelevant to your case P&L.
Most firms know this.
What they miss is that the Final Fee is owed at a specific procedural moment, and the defense can structure its conduct to avoid triggering it on a tranche. If the defense settles or withdraws a case before the Final Fee triggers, that case never enters the bucket.
On a campaign where 30% of cases settle pre-Final-Fee, the defendant's exposure model isn't $600 per case across 6,500 cases. It's $600 across roughly 4,550 cases. The negotiating leverage that comes from "we will trigger $3.9 million in Final Fees" is actually "we will trigger $2.7 million."
If your settlement model is built on the gross number, you've overstated your leverage by 30% to 35%.
Error 3: The 13% Case Management Fee gets forgotten on JAMS
If your matter ends up at JAMS instead of AAA (75 or more similar Demands triggers JAMS's mass arb rules), there's a 13% Case Management Fee on projected professional fees that doesn't exist in the AAA structure.
It doesn't show up in the headline JAMS filing fees ($5,000 business and $2,500 claimants total, not per case). It shows up later, calculated against the arbitrator's projected billing.
On a matter with $1.2 million in projected arbitrator fees, that's $156,000 added to case cost. Half goes to one side, half to the other under the standard split. The plaintiff-side share is $78,000 nobody planned for.
I have seen exactly two firm-side fee models that captured this line correctly. Both belonged to firms that had been burned by it on a prior matter.
What the right model looks like
Build the fee schedule as a tiered calculator, not a per-case multiplier.
Run three scenarios.
One assumes 100% cohort progression. One assumes 8% Process Arbitrator culling in the first 500 (the variance from last week's piece on the new TCPA landscape). One assumes 30% pre-Final-Fee settlement.
The spread between scenario one and scenario three is your real fee exposure. Use the middle of that spread for your engagement letter math. The high end for your reserve. The low end for your worst-case settlement floor.
Stress-test against the actual schedule version. AAA updated its mass arb rules and fee schedule in January and April 2024. Check the version date on whatever PDF you're modeling from. There are still firms running estimates against the 2022 schedule because their case manager downloaded the rules once and never updated.
And if the defendant's clause sends you to NAM, ADR Services, or a custom protocol, throw the AAA and JAMS schedules out entirely. Those numbers don't apply. Build the model against the clause itself.
The number that actually matters
The AAA fee schedule isn't complicated. The schedule isn't the problem.
The problem is that mass arb fee modeling is a finance discipline, and most firms still treat it as a paralegal task. The case manager pulls the rules, plugs numbers into a spreadsheet, hands it to the partner. The partner skims the bottom-line cost-per-claim and approves it.
Nobody is running the tier math.
Nobody is running the Process Arbitrator culling scenario.
Nobody is checking whether the defendant's clause even points to AAA in the first place.
The firms that do this well treat the fee model the way M&A treats a financial model. Multiple scenarios. Sensitivity tables. Updated source documents. A second set of eyes.
It's not that the AAA schedule is tricky.
It's that "$50 per case" feels like an answer.
It isn't.
It's an input.
If you want a tiered, scenario-modeled fee analysis on your next mass arb matter before you sign the engagement letter, we run that for plaintiff firms. Reach Kasia at (800) 800-4045 or visit massarb.groupsettle.com.