30 Day Yield Calculator: Compare Funds the Way Prospectuses Actually Do
Enter a fund's recent income and price, choose your method, and see the standardized annualized yield you'd find quoted in a real fund prospectus.
Dividends and interest earned by the fund over the last 30 days, after fund expenses if using the standardized method.
Only used in the standardized method, since it subtracts expenses before annualizing.
The last day of the 30 day period you're calculating for.
Why Fund Yields Need a Standardized Formula at All
Left to their own devices, funds could calculate and advertise yield in whatever way made their numbers look best, which is exactly the kind of inconsistency that makes comparing two funds nearly impossible. A standardized 30 day yield formula fixes that by forcing every fund to report using the same method, the same 30 day window, and the same treatment of expenses, so a number from one fund company means the same thing as a number from a competitor. That comparability is really the entire point of the calculation.
The Math Behind the Standardized Method
The standardized approach starts with net investment income after subtracting fund expenses, divides that by the average number of shares outstanding and the share price, then applies a compounding step that assumes the same rate repeats over six periods before doubling it to reach an annual figure. That compounding assumption is what separates this method from a naive calculation, it reflects the idea that reinvested income compounds rather than just adding up in a straight line, which produces a more realistic annualized comparison across funds.
Why the Simple Method Still Has Its Place
Not every situation calls for the full standardized formula, sometimes you just want a rough annualized sense of a short-term income stream without wading into compounding assumptions. The simple method here does exactly that, dividing income by price and multiplying by twelve to stretch a 30 day figure across a full year. It won't match an official prospectus number, but it's a fast, honest approximation for quick comparisons, which is why this calculator keeps both methods available side by side rather than forcing one approach on everyone.
Reading the Gap Between the Two Numbers
When you run the comparison mode, you'll usually see the standardized yield come in a touch higher than the simple method, purely because of the compounding assumption baked into the formula. If that gap looks unusually large, it's often worth double-checking your expense figure, since a large expense ratio pulls the standardized number down noticeably more than it affects the simple calculation.
What Actually Moves a Fund's Yield Over Time
Interest rate changes are the biggest driver, since bond funds holding newer, higher-yielding debt naturally show a higher 30 day yield than one still holding older, lower-rate bonds. Expense ratios matter too, a leaner fund keeps more income for shareholders after costs. Credit quality plays a role as well, funds willing to hold riskier debt often show a higher yield specifically because investors demand more compensation for that added risk, not because the fund is simply performing better.
Standards This Tool Follows
| Reference | How it's applied here |
|---|---|
| ISO 8601 | Your period end date is entered and processed in the unambiguous YYYY-MM-DD format |
| ISO 4217 | All monetary figures work with standard international currency conventions |
| WCAG 2.1 AA | Every field is labeled, keyboard accessible, and contrast-checked |
Frequently Asked Questions
What is a 30 day yield?
It's a standardized measure of a fund's income over the most recent 30 days, annualized so funds can be compared consistently rather than judged on a single raw monthly figure.
How is the SEC 30 day yield formula different from a simple calculation?
The standardized version subtracts expenses first and applies a compounding assumption before annualizing, producing a different, generally more conservative and comparable figure than simply multiplying monthly income by twelve.
Why do two funds with similar holdings show different 30 day yields?
Expense ratios are usually the biggest factor, since lower costs leave more income for the standardized formula to annualize, alongside smaller differences in exact holdings and share pricing.
Is a higher 30 day yield always better?
Not necessarily, since a higher figure can also reflect greater credit risk or longer duration within the fund rather than simply a better deal, so it's worth looking at what the fund actually holds.