State Street SPDR Bloomberg 1-3 Month T-Bill ETF (BIL)

The State Street SPDR Bloomberg 1-3 Month T-Bill ETF (ticker BIL) is perhaps the simplest exchange-traded fund in existence: it holds a portfolio of United States Treasury bills that mature within one to three months. Treasury bills are the shortest-dated debt instruments the US government issues, backed by the full faith and credit of the United States, and rolled over constantly by the fund to maintain the narrow maturity window. For investors seeking a place to park cash at a rate of return better than a traditional savings account but with virtually no credit or duration risk, BIL serves as a liquid, transparent alternative to money-market funds.

The fund’s appeal rests on a single principle: stability with a modest yield. Because the fund only holds Treasury bills that will mature within weeks, the value of the fund’s shares moves almost imperceptibly. If you hold a Treasury bill to maturity, you receive your principal back in full — there is no duration risk, the way there is with longer bonds. BIL passes that property on to shareholders. The price per share fluctuates by cents or fractions thereof, and only the yield earned during your holding period determines your return.

How BIL works day to day

The fund maintains a continuously rolling portfolio of Treasury bills. As individual T-bills near their maturity date, they mature and are paid off, so the fund receives cash. That cash is immediately reinvested in new Treasury bills further out the maturity curve (but still within the one-to-three-month window). This rolling ensures the fund always holds bills across a range of maturity dates, none older than ninety days.

When you buy BIL, you own a proportional stake in that entire rolling portfolio. You receive your share of whatever yield those Treasury bills earn each day, and that tiny daily accrual compounds. The fund distributes this income daily, and many brokers automatically reinvest those distributions, so you never see the drip — it compounds silently in your account balance.

The fund holds only Treasury bills, which are auctioned by the US Treasury every week. No other holdings, no credit risk. BIL is essentially a diversified basket of ultra-short government debt, which means it offers the safety of Treasuries in a liquid ETF wrapper.

Yield and what drives it

The yield on Treasury bills is set by auction and fluctuates weekly based on demand and Federal Reserve policy. When the Fed is keeping short-term rates high, T-bill yields are high and BIL’s yield is attractive. When the Fed cuts rates and short-term yields fall, BIL’s yield falls with them — there is no interest-rate risk to lock in a return, because the bills constantly mature and roll into new ones at current market rates.

Over the past decade, BIL has served as a barometer of short-term rate movements. During the period from 2009 to 2021, when the Fed held short rates near zero, BIL’s yield was similarly minimal. After the Fed began raising rates in 2022, T-bill yields surged, and BIL’s yield climbed in turn. The fund delivers whatever the market rate for one-to-three-month Treasury debt is at any given time — no better, no worse.

This also means BIL is not a “set it and forget it” fixed-income choice. If you buy BIL when the Fed is about to cut rates, your yield will fall as those cuts happen. Conversely, if you buy BIL as the Fed begins raising rates, your yield will climb. The timing of your purchase matters for the income you receive afterward, even though the principal value of the fund stays rock-stable.

Why BIL instead of a money-market fund or savings account?

The appeal of BIL relative to other ultra-safe, liquid vehicles is transparency and structural simplicity. A traditional money-market fund holds Treasuries, CDs, commercial paper, and other short-term debt, and its value per share is fixed at $1 (regulators require this). Interest accrues invisibly and is added to your balance. With BIL, there is no fixed NAV. The share price moves (minutely) to reflect the daily gains and losses on the underlying Treasury bills as interest accrues. Some investors find this more transparent — the mark-to-market approach makes earnings visible in the price.

Against a traditional savings account at a bank, BIL offers Treasury yields (which are often higher) in exchange for a tiny amount of account structure — you need a brokerage account to hold an ETF. The trade-off appeals to anyone comfortable with trading ETFs.

BIL has no credit risk (US government debt is backed by the full faith and credit of the United States), and near-zero interest-rate risk (because bills roll constantly into new ones at current rates). The only risk of consequence is a collapse of the US dollar’s purchasing power due to inflation, but that affects a savings account equally.

Costs, trading, and distributions

BIL’s expense ratio is among the lowest of any ETF — measured in basis points (hundredths of a percent), it is small enough to be a non-issue. The fund trades on US stock exchanges with tight bid-ask spreads, so transaction costs for buying and selling are minimal.

The fund distributes its interest income daily in the form of an accrual to the fund’s net asset value. Some brokers will reinvest those distributions automatically; others may pool them differently. Check your broker’s documentation, but the effect is the same — the interest earned by the underlying Treasury bills flows through to you daily.

When BIL makes sense

BIL suits investors who need a safe, liquid place to hold cash temporarily, particularly when short-term interest rates are attractive (as they have been since 2023). It appeals to those saving for a purchase in the near term, holding cash between investments, or simply wanting the safest possible liquid asset that pays interest. It is also useful as an emergency-fund anchor in a brokerage account, replacing a savings account while capturing Treasury yields.

Longer-term investors in a low-rate environment might prefer a slightly longer-duration Treasury fund — a fund holding one-to-five-year Treasuries, for example — to capture a bit of yield-curve pickup. But for true liquidity and stability, BIL is hard to beat.

BIL is not appropriate for anyone seeking capital appreciation or willing to accept volatility for higher expected returns. It is a cash equivalent that trades on an exchange, not an investment vehicle.

Research and practical considerations

Start with the fund’s fact sheet and prospectus, both available on State Street’s website. The fact sheet shows the current holdings — the specific Treasury bills in the portfolio, their maturity dates, and their yields. This transparency is one of BIL’s defining features; you can see exactly what you own.

Compare BIL’s current yield against what your bank savings account or money-market fund offers. The difference is often substantial enough to justify the minimal structure required to hold an ETF. If rates are similar, your savings account may be more convenient.

Understand your tax situation. Treasury interest is exempt from state and local income tax in most jurisdictions, which can make BIL more attractive than a money-market fund holding taxable commercial paper or CDs. In a taxable account, that tax efficiency matters. In a tax-advantaged account (a 401k or IRA), it makes no difference.

Finally, recognize that BIL’s yield will move with changes in Federal Reserve policy. If the Fed begins cutting rates, BIL’s yield will fall in parallel. If rate cuts are in prospect, locking in current Treasury bill yields via BIL makes sense. If rates are expected to rise, waiting may offer a higher yield later.