Mercury, Brex, or Relay for Multi-Entity Sweep Accounts

Before comparing banks, be clear on the job: each legal entity needs its own ledger, its own approvers, and a way to sweep cash it doesn't need for near-term operating expenses into something that earns a return, without ever commingling funds that belong to a different entity. A parent holding company usually also needs a consolidated view across all of them, even though the money itself has to stay separated for audit and liability reasons.

Get this requirement list down first. It's the yardstick for judging any of the three banks below, and it's also what your auditors will ask about at year end. Say your structure is a parent plus two operating subsidiaries: you need three ledgers, three sets of approvers, and one dashboard the parent's controller can read without logging into three separate places.

Mercury lets you open a separate account for each legal entity and view them together from one login, with virtual sub-accounts inside each entity for earmarking cash (payroll, taxes, a specific vendor contract). Its treasury product sweeps excess balances into government money market funds or Treasury bills, entity by entity, so each subsidiary's swept cash stays attributed to that subsidiary rather than pooling at the parent level.

That separation is the main reason founders running two or three related entities gravitate here: you get yield without having to manually track whose money is whose. The tradeoff is that each entity still needs its own onboarding and its own compliance checks, so adding a fourth or fifth entity isn't instant.

Brex's cash management is built around Brex Cash, which sweeps into government money funds much like Mercury's does, but the product assumes a primary operating entity with card programs and bill pay layered on top of it. If your subsidiaries mostly exist to hold IP, run payroll in another country, or isolate a regulated product line, Brex's structure works better as one dominant entity with the others handled as satellite accounts than as several fully equal entities.

Companies that already run corporate cards through Brex tend to keep the sweep account there for the convenience of one dashboard, even when a bank-only option would be marginally simpler. That convenience matters less if your subsidiaries need equal, independent standing rather than a hub-and-satellite arrangement.

Relay's strength is volume of sub-accounts, up to twenty under one login, with fast internal transfers between them. It doesn't offer a native yield sweep the way Mercury or Brex do, so it's a better fit when your goal is clean bookkeeping segmentation across many thin entities (a franchise structure, a portfolio of small subsidiaries) than when the goal is maximizing yield on a large treasury balance.

Many finance teams pair Relay's sub-accounts for day-to-day operating cash with a separate brokerage or bank sweep for the yield piece, rather than expecting one platform to do both well. That split adds a login but keeps each tool doing the job it's actually built for.

The most common mistake in a multi-entity move isn't picking the wrong bank, it's migrating every entity at once. Move one entity first, run it alongside the old setup for a full billing and payroll cycle, and only then migrate the rest. Teams that migrate everything on the same weekend tend to discover a missed vendor ACH authorization or a stale payroll integration only after a payment bounces, which is a far more expensive way to find the same problem.

A safer migration sequence looks like this:

1. Pick one entity to migrate first and open its new account, keeping the other entities on the current setup for now.
2. Run that entity alongside the old setup for a full billing and payroll cycle before touching any other entity.
3. Use the overlap cycle to catch missed vendor ACH authorizations and stale payroll integrations while they are still easy to fix.
4. Migrate the remaining entities in stages once the first one has run cleanly, rather than all on the same weekend.

If you have two to four entities and want native yield on the swept balance, Mercury's per-entity treasury sweep is the more direct fit. If your card spend and bill pay volume already lives in Brex and your secondary entities are smaller satellites, keeping the sweep account there avoids adding a fourth login to reconcile. If you're managing a dozen or more thin entities and the priority is bookkeeping clarity rather than yield, Relay's sub-account count does more for you than either bank's treasury product.

How much you actually leave swept into yield instead of sitting liquid also depends on your burn multiple: a company burning cash faster than it adds new revenue needs a fatter unswept cushion than one that's closer to breakeven¹. For a closer look at card programs specifically across these three, see Mercury vs. Relay vs. Brex.