Using a Money Market Fund Inside an HSA

Many people view their Health Savings Account as a checking account, holding cash for near-term medical expenses. But if you have unspent HSA funds beyond your immediate needs, a money market fund offers a way to earn current yield while keeping the cash fully available for qualified medical expenses. The setup is straightforward, the tax and legal treatment is clean, and it can materially improve returns on HSA balances that might otherwise sit idle.

Why Money Market for HSA Cash

An HSA is a triple-tax-advantaged account: contributions are deductible, growth is tax-free, and withdrawals for qualified medical expenses are not taxed. Many people keep HSA balances in cash or a linked savings account earning negligible interest. But if your HSA provider offers brokerage access (most do), you can buy a money market fund to earn current yields.

The key insight is that money market funds are not bonds. They hold very-short-duration instruments—Treasury bills, short-dated commercial paper, and repurchase agreements—typically with an average maturity under 60 days. Interest-rate risk is minimal. If you need to liquidate for a qualified expense, you can do so in a day or sometimes the same day.

For someone who set up an HSA three years ago, maxed it out annually, but has only spent $2,000 on medical expenses, sitting on $5,000 or $10,000 in cash earning 0.01% is wasteful. That same balance in a money market fund earning 4.5% creates several hundred dollars in additional value annually, all tax-free.

How to Set It Up

Most HSA providers (Fidelity, Lively, TD Ameritrade, and others) offer self-directed brokerage accounts within the HSA structure. The process is:

1. Check your HSA custodian’s offerings. Some HSAs are limited to savings vehicles; others offer full brokerage. If your current custodian doesn’t, you can often roll the HSA to one that does without tax consequences.

2. Fund the brokerage subaccount. Transfer cash from your HSA cash balance to the brokerage account. This is an internal move, not a distribution, so there are no tax triggers.

3. Select a money market fund. Look for funds offered in the HSA platform. Common examples include Vanguard Federal Money Market Fund, Fidelity Treasury Money Market Fund, or Schwab Value Advantage Money Market Fund.

4. Place the order. Buy shares of the fund. Settlement typically occurs T+1 (next business day), though some platforms allow same-day liquidity.

5. Monitor and rebalance. As your HSA balance grows with contributions, decide how much to keep in money market versus cash or other investments.

If you need cash for a medical expense, simply liquidate shares of the fund. The proceeds return to your cash balance or directly pay the provider, depending on your HSA’s structure.

Yield and Rate Environment

The attractiveness of this strategy depends directly on the federal funds rate.

When the Fed holds rates near zero (as it did from 2009–2015 and briefly in 2020–2021), money market funds yield almost nothing, and the opportunity cost of leaving cash uninvested is minimal. But when rates rise—as they did sharply in 2022–2023—money market funds suddenly offer 4.5% to 5.5% yields, and the case for allocation becomes strong.

A $10,000 HSA balance earning 0.01% in cash generates $1 of annual income. The same balance in a 4.5% money market fund generates $450. Over five years, assuming the fund continuously rolls at 4.5%, that’s $2,250 in additional returns. For someone with a larger HSA balance or a longer time horizon before expenses, the compounding can be substantial.

Check the expense ratio of the fund. Institutional-class money market funds often charge 0.10% to 0.20% annually. A $10,000 position incurs $10–$20 in fees, but you’re still netting 4.3–4.4% if the fund’s gross yield is 4.5%. The math is straightforward.

Liquidity and Qualified Expense Risk

A common worry is: what if I need the money urgently and the fund is suspended?

Money market funds are extremely stable. They hold short-dated government and high-quality commercial instruments, and they are subject to strict regulatory limits on credit quality. A suspension or “gate” (preventing redemptions) has never happened at a major U.S. money market fund. Even during the 2008 financial crisis, when one reserve fund broke the buck, the SEC quickly implemented new rules and the fund was rescued.

More practically, liquidity is not a constraint. You can sell shares of a money market fund held in an HSA on any business day and have the proceeds back in your cash account or available for immediate payment of medical expenses within 24 hours, often sooner. This is far faster than waiting for a reimbursement check or an insurance claim.

The only scenario where you face a real delay is if your HSA provider imposes settlement delays on internal transfers or if you are trying to liquidate during a market closure. These are rare, and you can check your custodian’s policy in advance.

Allocation Strategy Within an HSA

Most people should hold a layered approach:

• Cash buffer (1–3 months of expected medical expenses): Keep 1–2 months’ worth of estimated annual medical spending in the HSA cash account. This covers routine copays, prescriptions, and unexpected doctor visits without forcing you to liquidate investments.

• Money market funds (3–12 months of buffer): Park 3–6 months of additional expected expenses in a money market fund. This balances yield and liquidity.

• Longer-term investments (surplus beyond 12 months): If your HSA has grown to a size where you’re confident you won’t spend the entire balance within a year, consider using the index fund or bond fund options to capture higher returns. An equity ETF is also allowed in an HSA and can offer growth for funds you plan to leave invested for decades.

Someone with a $15,000 HSA balance might keep $2,000 in cash, $5,000 in a money market fund earning ~4.5%, and $8,000 in a low-cost S&P 500 index fund for long-term growth.

Tax and Eligibility Reminders

Distributions from an HSA for qualified medical expenses are always tax-free, regardless of whether the funds came from cash, a money market fund, or a stock investment. You do not owe taxes when you liquidate the money market fund; you owe taxes only if you withdraw the proceeds for non-medical purposes before age 65.

Also: money market funds held in an HSA are treated identically to other HSA assets. There are no special rules or restrictions. The HSA custodian reports the balance on your annual tax statement, and that’s the extent of the documentation burden.

Choosing the Right Fund

When selecting a money market fund for your HSA, prioritize:

1. Expense ratio: Lower is always better. Aim for 0.15% or less. A 0.50% ratio eats heavily into your yield.

2. Credit quality: The fund should hold primarily Treasury bills and government repurchase agreements. Avoid funds that take excess credit risk in commercial paper. Your HSA should not be a venue for credit speculation.

3. Fund size: Larger funds (over $5 billion in assets) are more stable and less prone to closure or merger.

4. Availability in your HSA: Not all funds are available at all custodians. Check what your HSA provider offers before opening the account or consider rolling to a custodian with broader fund options.

Vanguard, Fidelity, and Schwab offer solid, low-cost options across most HSA platforms.

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