Reviewed and corrected September 20, 2026: This article replaces an earlier example that mixed a six-month bill with a full year of savings interest and presented unsourced tax brackets. The example below compares annualized rates only; it does not claim a current offered yield or a one-year cash return from a shorter bill.
A high-yield savings account and a Treasury bill can both hold short-term funds, but their quoted rates, tax treatment, insurance, and access to cash differ. The best comparison uses actual offers available to you, the same holding period, and your own tax situation. The rates below are hypothetical teaching inputs.
Start with the quoted rate and holding period
A bank’s savings annual percentage yield (APY) accounts for its stated compounding convention, but the bank can change the rate. A bill is purchased at a price determined at auction or in the market; the difference between its purchase price and the amount paid at maturity is its interest. Treasury bills have terms measured in weeks, including 26- and 52-week issues. An annualized bill yield is a rate quotation, not a promise that a 26-week bill will generate a full year’s interest without reinvestment. TreasuryDirect’s bill FAQ explains maturities and payment at maturity. Our Treasury securities guide explains the broader maturity choices.
How does the tax difference affect a comparison?
IRS Topic 403 says interest from U.S. Treasury bills, notes, and bonds is federally taxable but exempt from state and local income taxes. 31 U.S.C. § 3124 provides the underlying exemption for federal obligations, subject to its terms. Bank deposit interest is generally taxable income; whether and how state tax affects a particular saver depends on that jurisdiction and filing circumstances.
Consider hypothetical annualized quotations: 5.00% savings APY and 4.80% bill investment yield. For a simplified illustration, assume a 24% federal marginal rate, either a 0% or a 5% marginal state rate on bank interest, no local tax, and no interactions or deductions between tax systems. Hold each quoted rate constant for comparison. These are assumed rates and tax inputs, not current offers or state tax schedules.
| Assumed state marginal tax on bank interest | 5.00% savings APY, simplified after tax | 4.80% bill yield, simplified after tax |
|---|---|---|
| 0% | 3.800% | 3.648% |
| 5% | 3.550% | 3.648% |
The simplified arithmetic is savings rate × (1 − federal rate − assumed state rate), and bill yield × (1 − federal rate). At the assumed 5% state rate, a savings APY of about 5.14% would match the bill’s 3.648% simplified after-tax annualized rate: 3.648% ÷ (1 − 0.24 − 0.05). This model omits compounding differences, federal/state tax interactions, other taxes, fees, and changing rates. An actual 26-week bill’s dollar payoff must be calculated from its purchase price and maturity value over those 26 weeks; it is not the full-year amount shown by an annualized rate.
What protects the principal?
FDIC deposit insurance covers eligible deposits at an FDIC-insured bank up to $250,000 per depositor, per insured bank, for each ownership category. Accounts at a federally insured credit union have separate NCUA share insurance, subject to its own ownership rules. Check the actual institution and account: an investment or a fintech interface is not automatically an FDIC-insured bank deposit.
U.S. Treasury bills are direct government obligations and are not FDIC-insured deposits; the FDIC’s insured-deposits guide makes that distinction. Holding a bill to maturity differs from selling early: its market price can change with rates, and transaction terms may affect proceeds.
How soon can you get the money?
Savings withdrawal methods and transfer timing depend on the bank and account. A bill pays its face amount at maturity; selling before then requires a market transaction. If the bill is held in TreasuryDirect, TreasuryDirect says it must first be transferred to a bank, broker, or dealer, and TreasuryDirect generally imposes a 45-day holding period before transfer. A four-week bill held there therefore cannot be sold before maturity through that path. Compare these practical access rules, and any broker fees or bid-ask spread, alongside the rate.
A useful decision worksheet records the actual bank APY and insurance status, the bill’s price, yield and maturity date, the date cash may be needed, and applicable tax treatment. Recalculate for the same time horizon. Neither a hypothetical rate advantage nor the word “safe” substitutes for those checks.
Sources
- IRS Topic 403: Interest Received and 31 U.S.C. § 3124 — Treasury interest tax treatment.
- TreasuryDirect bill FAQ and selling guidance — bill maturity and access.
- FDIC deposit insurance, insured-deposits guide, and NCUA share insurance — different protections.
Educational illustration only; not individualized investment or tax advice. Rates and eligibility should be verified for the date and account in question.