VMFXX vs SGOV: Settlement Cash or a T-Bill ETF?

Overview

SGOV and VMFXX are both short-duration, government-backed fixed-income securities that sit at the ultra-safe end of the yield curve. SGOV is an ETF tracking Treasury bills maturing in three months or less; VMFXX is a money market mutual fund that holds government securities and repo agreements backed by Treasuries or cash. Both offer similar yields around 3.65–3.66% but differ fundamentally in structure, stability commitment, and intended use.

How they differ

The biggest difference is price stability. VMFXX maintains a constant $1.00 net asset value by design—it's a money market fund that adjusts its credit quality and duration to keep NAV flat. SGOV trades like any ETF, with a market price that fluctuates ($100.69 at snapshot) as Treasury bill yields and valuations shift. That means SGOV has minimal interest-rate risk for ultra-short Treasuries but real mark-to-market volatility; VMFXX sacrifices that flexibility to guarantee you never lose principal to price moves. SGOV charges 0.09% annually; VMFXX costs 0.11%, a small but meaningful difference on large balances. SGOV is index-based and transparent; VMFXX is actively managed to maintain NAV stability and serves as the default settlement fund for Vanguard brokerage accounts, making it a de facto cash holding vehicle for Vanguard investors.

Who each is best for

• SGOV: Fits investors who can tolerate daily NAV swings in exchange for slightly lower fees, hold Treasury bills directly as a fixed-income position, and want transparent index exposure to the shortest-duration government securities.

• VMFXX: Designed for investors prioritizing a locked $1.00 share price and maximum convenience—especially those who hold Vanguard brokerage or mutual fund accounts and want seamless cash sweep functionality without worrying about price fluctuations.

Key risks to know

• Interest-rate sensitivity in SGOV: Although duration is minimal, rising rates cause Treasury prices to fall, and SGOV's market price will reflect that. VMFXX avoids this by adjusting holdings to maintain its $1.00 target, shifting the interest-rate timing risk to the fund's managers rather than shareholders.

• Repo and credit risk in VMFXX: Money market funds rely on short-term repo agreements and overnight funding markets. While VMFXX's holdings are backed by U.S. government collateral, a severe funding dislocation (rare but possible) could impair liquidity or require the fund to break its $1.00 NAV, known as "breaking the buck"—a risk SGOV doesn't face because it holds actual Treasury bills outright.

• Yield compression at short maturity: Both funds invest in instruments maturing in weeks to months. If Treasury yields decline significantly, income will fall sharply at the next rollover or distribution reset; there's no yield cushion or duration extension to offset rate drops.

• Opportunity cost if rates rise further: Locking into 3.6% today leaves room to miss out if yields climb higher over coming months. VMFXX's active management can adjust duration modestly to capture some upside, but SGOV is fully indexed and won't.

Bottom line

If you value fees, simplicity, and don't mind seeing your share price bounce with Treasury yields, SGOV's 0.09% expense ratio and transparent index approach has an edge. If you want a true cash replacement with guaranteed $1.00 stability and are willing to pay 2 basis points more annually, VMFXX's constant NAV and Vanguard integration make it the natural default. Past performance of either doesn't predict future rates or yields.