Money Market Mutual Funds, Repurchase Agreements, and State/Local Tax Exemptions

If you live in a state that taxes interest income, you may know that can significantly alter the net after-tax yield on your investments. This is because direct U.S. government obligations like Treasury bills and bonds are generally exempt from taxation in most states. For example, if a Treasury bill is yielding 5% but is exempt from a 8% state income tax, that would make it the equivalent after-tax yield of a bank CD at 5.65% APY (assuming 22% federal tax rate). That’s a pretty big difference! See Treasury Bond vs. Bank CD Rates: Adjusting For State and Local Income Taxes for details.

Money market mutual funds (available in most brokerage accounts) usually hold part of their portfolio in securities that count as US government obligations (USGO). (See Vanguard Federal Money Market Fund: How to Claim Your State Income Tax Exemption.)

For the 2022 tax year, Vanguard Federal Money Market Fund (VMFXX) had about 38% in USGOs, but the Vanguard Treasury Money Market Fund (VUSXX) had 100% in USGOs (source). As long as the yields were pretty close, your after-tax yield would be much higher with the Treasury Money Market fund if you were in a high state/local tax bracket. (VMFXX is the default sweep though, so you’d have to manually purchase VUSXX.)

However, these USGO percentages can change from year to year, and it is happening in 2023. A quick rewind – here is a list of what is and is not exempt from state and local taxes.

*Investments in U.S. government obligations may include the following: Federal Farm Credit Banks, Federal Home Loan Banks, the Student Loan Marketing Association, the Tennessee Valley Authority, the U.S. Treasury Department (bonds, notes, bills, certificates, and savings bonds), and certain other U.S. government obligations. GNMA, FNMA, Freddie Mac, repurchase agreements, and certain other securities are generally subject to state and local taxes.

In particular, even though the Vanguard Treasury Money Market Fund has “Treasury” in its name, it doesn’t only hold Treasury Bonds. It can also hold something called repurchase agreements (“repos”). These are often sold on a very short-term basis (overnight or less than 48 hours). While a repo is considered a very, very safe loan backed by government securities, it is not itself a government security, which means the income it creates is taxable at the state and income level.

As of July 2023, here is the percentage of repurchase agreements held by these two example money market funds: 58% for VMFXX and 34% for VUSXX. This would suggest that the USGO number for VUSXX will be significantly less than 100% for 2023, although VUSXX still holds less repos than VMFXX.

For an in-depth comparison, “retiringwhen” of the Bogleheads forum has created a detailed Google Spreadsheet that tracks and calculates the after-tax yields for several different money market funds from Vanguard and Fidelity. I would point out that the low expense ratio of Vanguard funds makes their money market funds consistently better than Fidelity money market funds across the board.

I also hold some Treasury bonds directly and while laddering isn’t that much hassle, recently I have been considering simplifying to VMFXX and VUSXX as the go-to place for my liquid cash savings account. For now, the tax-equivalent yield is higher than nearly all other savings accounts due to my high state-tax situation. I am also looking at ETFs that hold mostly T-bills like SGOV and BIL.

Bottom line. If you want to be precise, the full-geek DIY investor with state/local income taxes has to take into account the percentage of repos in their money market fund portfolios in order to calculate the true tax-equivalent yield to compare against other cash alternatives.

[Top image credit – Wikipedia]