SEC 30 Day Yield Explained

I was asked what is the SEC 30 day yield. Here is the abridged definition from Wikipedia.

30-day yield is a standardized yield calculation for bond funds. It's formula is specified by the U.S. Securities and Exchange Commission (SEC). The formula translates the bond fund's current portfolio income into a standardized yield for reporting and comparison purposes.

Because the 30-day yield is a standardized mandatory calculation for all United States bond funds, it serves as a common ground comparison of yield performance. Its weakness lies in the fact that funds tend to trade actively and do not hold bonds until maturity. In addition, funds do not mature. For this reason, analysts often consider a distribution yield to be a better measure of a fund's income-generating potential.

United States money market funds report a 7 Day SEC Yield. The rate expresses how much the fund would yield if it paid income at the same level as it did in the prior month for a whole year. It is calculated by taking the sum of the income paid out over the period divided by 7, and multiplying that quantity by 36500 (365 days x 100).

The SEC yield calculation for a bond fund is essentially a yield to maturity for the bond portfolio. Because bond funds trade actively and prices fluctuate, the rate may not be a good indicator of future results. However, because the calculation is standardized, it provides a good comparison measure for funds.

For you formula wonks Wikipedia says the calculation for SEC 30-day yield is:
Yield = 2[{(a-b)/cd+1}^6-1] Where:
a = dividends and interest
b = accrued expenses
c = average daily number of outstanding shares that were entitled to distributions
d = the maximum public offering price per share on the last day of the period

So there you have it.