7-day yield: what a money market fund’s headline number measures

The 7-day yield is the income a money market fund earned over the past seven days, after expenses, expressed as an annual rate. It is the number at the top of every fund page. This site starts from it, then ranks funds by what you keep after tax. The formula comes from the Securities and Exchange Commission’s rules for fund advertising: take the change in value of a hypothetical account holding one share at the start of the period, leave out capital gains and losses, divide by the starting value, and multiply by 365/7. Because a money fund keeps its price at $1.00 and pays its income as daily dividends, the result is close to the fund’s income of the week, annualized. On the last filed day, Vanguard Federal (VMFXX) reported 3.88%, which means a week of income at an annual pace of 3.88% of the balance. It is a statement about the past week, not a promise about the next year: if short-term rates move, the yield follows within weeks. It is also a simple rate. Dividends credited daily and reinvested earn their own dividends, so over a year a steady 3.88% would grow a balance by about 3.96%, the effective yield.

Net and gross: what expenses take

Every Form N-MFP report carries two versions of the yield. The gross 7-day yield is what the portfolio earned before the fund deducted its expenses; it is reported once for the whole fund. The net 7-day yield is reported for each share class, after that class’s expenses and any fee waiver. The difference between the two is the cost of owning the class, measured in yield. On the latest filings, Fidelity Government Money Market (SPAXX) had a gross yield of 3.97% and a net yield of 3.55%, a gap of 0.42%; Vanguard Federal had 3.99% and 3.88%, a gap of 0.11%. Across the 283 share classes in the data where both figures are available, the average gap was 0.42%. Two classes of the same fund hold the same portfolio and show the same gross yield, so any difference in their net yields is cost alone. That is why this site shows the gap, under the name expense drag, on every fund page.

The expense ratio in a prospectus measures the same thing over a fiscal year. The gap between gross and net yields measures it on one day, and includes waivers in force on that day. When rates were near zero, many funds waived large parts of their fees to keep net yields above zero, and the gap shrank; with rates well above zero, waivers matter much less, and the gap shows the full cost.

Why the yield trails market rates

A money fund holds Treasury bills, agency notes, repurchase agreements and, for prime funds, bank and company paper, with maturities from one day to about a year. Its income on any day is the average rate on all those holdings, many bought days or weeks earlier. When the Federal Reserve moves its policy rate, overnight repo reprices the next morning, but a 3-month bill bought last month keeps its old rate until it matures. The weighted average maturity tells you how slow the fund will be: a fund at 20 days follows quickly, a fund at 50 days lags. The 7-day yield adds its own delay, since it averages a full week of income. Over the months on file, VMFXX moved from 3.57% on June 1, 2026 to 3.88% on October 30, 2026.

The chart also shows a second pattern. Vanguard’s municipal fund VMSXX swung over a range of 1.95% in the same months, against 0.33% for VMFXX. Municipal money funds hold variable-rate notes whose rates reset weekly on an index that reacts to flows into and out of tax-exempt funds, and to the calendar of tax payments. Their 7-day yield is noisier, and a single week says less about the coming month than it does for a government fund.

Comparing the 7-day yield with other rates

The 7-day yield compares cleanly with a Treasury bill’s coupon-equivalent rate, which the Treasury publishes every business day: both are annualized simple rates on a 365-day year. On November 6, 2026, the 4-week bill was at 3.95%. A savings account quotes an APY (annual percentage yield), which compounds; put the two on the same basis before comparing: the calculator above shows the effective version of a 7-day yield, and the savings comparison on this site turns the bank’s APY back into a simple rate, so the fund keeps the figure shown in every ranking. The 30-day SEC yield that bond funds and exchange-traded funds publish is a different measure, based on a month of income and on the yield to maturity of the holdings; it is close to a money fund’s 7-day yield for funds that hold only bills, but the two are not the same calculation.

None of these rates is what you keep. Money fund dividends are taxed as ordinary income, federally and, except for the share from U.S. obligations, by your state. A fund paying 3.55% can leave less after tax than one paying a few hundredths less, depending on what it holds. A municipal fund paying 2.27% owes no federal tax and has to be compared on a tax-equivalent basis. That is the purpose of the after-tax yield this site computes from the same filed figures.

Where the figure comes from on this site

The yields here are the daily 7-day net yields that each fund reported in its monthly Form N-MFP filing, for every business day of the month. The latest month in the data ends on October 31, 2026; the reports were filed between November 3, 2026 and November 6, 2026. A fund company’s own page shows a more recent figure, updated every business day. The two will match on the filed date and drift apart after it. This site uses the filed figure because it is the only one available for every fund on the same date, from the same source, without depending on how each company presents its numbers. On $10,000, the difference between two funds 10 basis points apart (0.10 percentage point) is $10 a year before tax: worth knowing, and worth checking against the fund’s current figure before moving money.