SGOV vs BIL vs TLT: 30-Day SEC Yield vs Distribution Yield Math & ETF Fee Drag Analysis (2026)

30-Day SEC Yield refers to a standardized net annualized yield metric mandated by the SEC that deducts fund expense ratios from 30-day portfolio income.

Fixed-income ETF net inflows reached $446.2 billion year-to-date through Q3 2026, with ultra-short U.S. Treasury bill funds capturing 64.5% of total government bond ETF creations [Monthly ETF Flows Report, Investment Company Institute (ICI), 2026-09-30]. While benchmark 3-month U.S. Treasury bill yields stand at 4.34% [3-Month Treasury Constant Maturity Rate DGS3MO, Federal Reserve Bank of St. Louis (FRED), 2026-10-16] and the 10-year Treasury par yield trades at 4.18% [Daily Treasury Par Yield Curve Rates, U.S. Department of the Treasury, 2026-10-16], income allocators face a critical quantitative choice between zero-duration cash proxies (SGOV, BIL, USFR) and duration-sensitive sovereign bond ladders (IEF, TLT).

Expense ratio fee drag directly determines net realized return across identical U.S. Treasury portfolios because sovereign coupon and discount accretion rates are fixed by auction clearing prices. Across a $100,000 allocation compounding at a 4.35% gross Treasury rate [Daily Treasury Bill Rates, U.S. Department of the Treasury, 2026-10-16], a 10.56 bps annual fee spread between a 3.00 bps net expense ratio and a 13.56 bps net expense ratio reduces 10-year terminal wealth by $1,482 [ETFYield Lab Expense Ratio Calculator, 2026-10-20].

Core Definitions: Yield Metrics, Duration, and Fee Drag

• 30-Day SEC Yield: 30-Day SEC Yield is defined as the standardized annualized net investment income earned by a mutual fund or ETF over the preceding 30-day period—calculated on a yield-to-maturity basis for all portfolio debt securities minus accrued management fees and operating expenses—divided by the maximum offering price per share on the last day of the period [Form N-1A Item 26(b)(4), U.S. Securities and Exchange Commission (SEC), 2026-10-15].
• Trailing 12-Month (TTM) Distribution Yield: Trailing 12-Month Distribution Yield refers to the backward-looking ratio of total cash distributions paid per share over the trailing 365 calendar days divided by the current net asset value (NAV) per share [Investor Bulletin on Bond Funds, SEC, 2026-10-01].
• Modified Duration: Modified Duration refers to the percentage change in a fixed-income security's price for a 100 basis point (1.00%) parallel shift in yield, calculated as Macaulay Duration divided by $(1 + \text{YTM}/f)$ [Fixed Income Analytics Standard, SEC / MSRB, 2026-10-01].
• ETF Fee Drag: ETF Fee Drag is defined as the cumulative reduction in compound portfolio value caused by daily accrual of the annual net expense ratio, bid-ask execution spreads, and cash drag relative to a zero-fee benchmark index [Form N-1A Fee Table Instructions, SEC, 2026-10-15].

Quantitative Formula: 30-Day SEC Yield vs. Distribution Yield

The U.S. Securities and Exchange Commission mandates that all registered open-end investment companies and ETFs compute 30-Day SEC Yield using the standardized Form N-1A equation [Form N-1A Item 26, SEC, 2026-10-15]:

$$\text{30-Day SEC Yield} = 2 \times \left[ \left( \frac{a - b}{c \times d} + 1 \right)^6 - 1 \right]$$

Every variable in the statutory SEC formula enforces strict accrual accounting over a 30-day window [Form N-1A Item 26, SEC, 2026-10-15]:

1. $a$ (Dividends and Interest Earned): Includes yield-to-maturity amortization of market discounts and accretions on zero-coupon U.S. Treasury bills over the 30-day period.
2. $b$ (Accrued Expenses Net of Reimbursements): Deducts the exact 30-day slice of the ETF's annual net expense ratio, meaning a 13.56 bps fee directly lowers the reported 30-Day SEC Yield by 13.56 bps relative to gross portfolio YTM.
3. $c$ (Average Daily Shares Outstanding): Measures the mean share count eligible for distributions during the 30-day window.
4. $d$ (Maximum Offering Price / NAV per Share): Captures the closing share price on the final day of the 30-day calculation period.

When the Federal Open Market Committee (FOMC) adjusts its target policy rate by 50 bps [Federal Reserve H.15 Selected Interest Rates, FRED, 2026-10-16], 0–3 month T-Bill ETFs turn over roughly 33% of their underlying bill maturities every 30 days. Consequently, the 30-Day SEC Yield reflects the new Treasury auction rate within 30 to 45 days, whereas the TTM Distribution Yield remains anchored to 11 months of historical payouts, overstating forward income by 40 bps to 85 bps after rate cuts [Daily Treasury Bill Rates, U.S. Department of the Treasury, 2026-10-16].

U.S. Treasury ETF Benchmark Comparison Table (2026)

The following table compares the five primary U.S. Treasury ETFs across maturity buckets, net expense ratios, 30-Day SEC Yields, modified durations, and 10-year fee drag on a $100,000 allocation [SEC EDGAR N-1A Filings & U.S. Treasury Yield Curve Data, 2026-10-16]:

Data Source: SEC Form N-1A Prospectus Filings (sec.gov), U.S. Department of the Treasury Daily Par Yield Curve (home.treasury.gov), and FRED Series DGS3MO / DGS10 / DGS30 (fred.stlouisfed.org) as of 2026-10-16.

Duration Convexity vs. T-Bill Ladder Rollover Mechanics

Rolling a 3-month Treasury bill ladder via SGOV or BIL isolates pure short-rate carry with near-zero mark-to-market volatility. Because SGOV maintains an effective duration of 0.09 years [SEC Form N-PORT Filing, SEC EDGAR, 2026-09-30], a sudden 100 bps upward shock in short-term yields produces a theoretical NAV drawdown of just -0.09% (-$90 per $100,000), which is recouped in 7.6 calendar days of higher coupon accretion at a 4.31% SEC yield [ETFYield Lab Bond Yield & Duration Calculator, 2026-10-20].

By contrast, TLT carries a modified duration of 15.82 years and a convexity of +3.18 [SEC Form N-PORT Filing, SEC EDGAR, 2026-09-30]. Using the second-order Taylor series bond price approximation:

$$\frac{\Delta P}{P} \approx (-\text{Duration}_{\text{mod}} \times \Delta y) + \left( \frac{1}{2} \times \text{Convexity} \times (\Delta y)^2 \right)$$

• +100 bps Long-End Yield Shock ($\Delta y = +0.01$): TLT experiences a price change of $(-15.82 \times 0.01) + (0.5 \times 3.18 \times 0.0001) = -15.82\% + 0.16\% = -15.66\%$ (-$15,660 per $100,000), wiping out 3.57 years of its 4.38% 30-Day SEC Yield [Daily Treasury Par Yield Curve, U.S. Department of the Treasury, 2026-10-16].
• -100 bps Long-End Yield Rally ($\Delta y = -0.01$): TLT captures a positive price appreciation of $(+15.82\%) + (+0.16\%) = +15.98\%$ (+$15,980 per $100,000), plus its 4.38% annualized coupon yield, delivering a 12-month total return of +20.36% [ETFYield Lab Bond Yield & Duration Calculator, 2026-10-20].

Frequently Asked Questions

Q1: Why does 30-Day SEC Yield differ from 12-Month Trailing Distribution Yield on Treasury ETFs?

30-Day SEC Yield calculates the annualized yield-to-maturity of the underlying bonds held over the most recent 30-day period after deducting the fund's expense ratio [Form N-1A Item 26, SEC, 2026-10-15]. Trailing 12-Month (TTM) Distribution Yield sums actual cash dividends paid over the past 365 days divided by current NAV, causing it to lag by up to 11 months during Federal Reserve interest rate cuts or hikes [FRED EFFR Benchmark Data, Federal Reserve Bank of St. Louis, 2026-10-16].

Q2: How much does a 10 bps ETF expense ratio difference cost on a $100,000 T-Bill ladder over 10 years?

Assuming a 4.35% gross Treasury bill return [Daily Treasury Bill Rates, U.S. Department of the Treasury, 2026-10-16], an ETF charging 3 bps (0.03%) grows $100,000 to $152,649 over 10 years, whereas an ETF charging 13.56 bps (0.1356%) grows to $151,167—a direct compounding fee drag of $1,482, or 148.2 bps of starting principal [ETFYield Lab Expense Ratio Calculator, 2026-10-20].

Q3: When should fixed-income investors rotate from ultra-short ETFs (SGOV, BIL) into intermediate or long duration (IEF, TLT)?

Ultra-short ETFs like SGOV carry a modified duration of 0.09 years, losing less than 0.09% in NAV if yields rise by 100 bps [Fund Disclosure Data, SEC EDGAR, 2026-10-15]. Extending into IEF (7.14 years modified duration) or TLT (15.82 years modified duration) is quantitatively justified only when the 10-year to 3-month Treasury term spread compensates for convexity risk or when FOMC rate cuts reduce front-end reinvestment yields below the 10-year par yield of 4.18% [Daily Treasury Par Yield Curve, U.S. Department of the Treasury, 2026-10-16].