What Is a Sweep Money Market Fund in a Brokerage Account?
Cash that lands in a brokerage account, whether from a sale, a dividend, or a deposit, rarely just sits idle. Most brokerages automatically move it somewhere, and a sweep money market fund is one common destination.
The short answer
A sweep money market fund is the default holding place many brokerages use for uninvested cash in an account, automatically moving, or “sweeping,” that cash into a money market fund so it can earn a yield instead of sitting idle. When the account holder buys a security or withdraws money, shares of the sweep fund are automatically sold to cover it.
How the mechanics generally work
Rather than leaving cash uninvested, a brokerage typically links each account to a designated sweep vehicle, often a money market fund, and any cash balance above a small threshold moves into it automatically at the end of each business day. The process runs in the background; the account holder doesn’t need to place a separate trade to move cash in or out of the sweep fund. This is a specific application of the broader concept covered in a piece on what a sweep account does more generally.
Why the yield and fees can vary
Not every brokerage uses the same sweep vehicle, and not every sweep fund pays the same yield after its expense ratio is factored in. Some brokerages offer higher-yielding sweep options as an upgrade or for larger balances, while others default to a lower-yielding option unless the account holder actively chooses otherwise. The size of the expense ratio attached to a given sweep fund is one factor behind why two brokerages, or even two account tiers at the same brokerage, can pay noticeably different rates on cash that looks otherwise identical.
What distinguishes a sweep fund from other money market funds
- It’s chosen for the account holder, by default. Unlike buying a specific money market fund deliberately, a sweep fund is often the automatic option unless something else is selected.
- It shares the general risk profile of similar funds. A sweep fund is still a fund, not a bank deposit, so it typically doesn’t carry deposit insurance the way a bank account would, though some brokerages also offer insured bank-sweep alternatives with different mechanics.
- Its holdings follow the same category rules. Depending on the specific fund, it may hold government securities, a broader mix as described in a look at prime versus government money market funds, or another category entirely.
- It’s usually disclosed, but easy to overlook. Account paperwork typically names the default sweep vehicle, though many account holders never read that section closely.
What to weigh
Since sweep options and their yields can differ meaningfully between brokerages, and sometimes between account types at the same brokerage, checking what the current default actually pays, and whether a higher-yielding alternative is available within the same account, is a quick way to see whether cash sitting between trades is earning what it reasonably could.
The takeaway
A sweep money market fund turns idle brokerage cash into something that at least earns a return while it waits to be used. The specific fund, its yield, and its fee structure differ by provider, which makes it worth a periodic look rather than an assumption that all sweep options are interchangeable.