Write a capacity decision memo that preserves uncertainty

Begin with the actual decision

Specify whether the question concerns a new allocation, an existing portfolio’s rebalance, a withdrawal, a change in execution window or a data-quality review. These decisions produce different order quantities and deadlines. A general request to find 'maximum capacity' is too ambiguous to calculate responsibly.

Name the version of the holdings, the decision timestamp, the eligible trading window and the owner of the decision. Then state the status in plain language: illustrative exploration, pending evidence, constrained operating scenario or independently supported empirical assessment. The status should reflect the evidence, not the polish of the chart.

A worked memo conclusion

Consider a hypothetical request to examine $40 million AUM with a 4% event trade, $20 million eligible volume, 3 bps fixed charges and k = 20 bps. The order is $1.6 million and participation is 8%. Modeled cost is 8.657 bps, or approximately $1,385.10. Portfolio drag is approximately 0.3463 bps.

If the chosen limits are 10% participation and 8 bps cost per traded dollar, participation passes but cost fails. A clear conclusion is: 'The $40 million illustrative scenario exceeds the chosen cost budget under these inputs; its conditional cost boundary is $31.25 million.' It is not: 'The strategy’s proven capacity is $31.25 million.'

Show alternatives and what each changes

One alternative is a two-session window. With otherwise fixed assumptions, participation becomes 4% and modeled cost becomes 7 bps, or $1,120. The trade remains unfinished longer. Another is a smaller event trade, which changes the intended portfolio transition. Neither alternative should be presented as a free capacity increase.

Show the associated decision consequence beside the numerical output. For the longer window, list the completion deadline and residual exposure. For the smaller trade, show the accepted target-weight deviation. For improved liquidity assumptions, cite the new evidence. This makes it difficult to solve a spreadsheet constraint by silently changing the investment task.

Separate execution due diligence from a model output

FINRA’s best-execution rule considers market conditions and order characteristics. A participation spreadsheet does not replace the review of a real broker’s routes, handling and execution quality. For a provider evaluation, ask for the scope and provenance of any capacity statement, including whether it concerns live accounts, simulated orders or a theoretical boundary.

Request representative records and clearly defined measurement periods rather than only a favorable average or a prestigious credential. The evidence should match the instruments and size being proposed. A strong result in another activity does not by itself establish executable capacity for this portfolio, and publication subject coverage does not establish a commercial product offering.

End with evidence-owned actions

A useful unresolved-action list identifies the missing item, why it matters, who can supply it and what decision depends on it. Examples include a lawful instrument-level volume history, a documented fee schedule, route-specific completion evidence or a review of overlapping account demand. Keep these actions concrete enough that a later reviewer can close them.

Preserve the memo and input export together with a date and version. Revisit the conclusion when weights, trade frequency, market conditions, execution arrangements or model assumptions materially change. A scenario result has no permanent validity simply because it was once approved. This template supports disciplined discussion; it does not certify capacity, recommend an allocation or claim that any provider manages the illustrative AUM.

Keep in the decision record

• State the decision and evidence status before the headline number.
• Show which constraint binds and what each alternative changes.
• Preserve exact missing evidence and the conditions for reconsideration.

Source notes

1. FINRA — Rule 5310, Best Execution and Interpositioning
2. Federal Reserve — Supervisory Guidance on Model Risk Management, April 2026

Sources inform the definitions and limitations. Scenario inputs and arithmetic are publication illustrations, not extracted market observations. Access checks are dated in the source inventory.

Continue the analysis