HYSA vs Treasury bills: which wins after state taxes?

Two of the safest places a US household can park cash both pay yields in the same neighborhood, are backed by the strongest guarantees available in dollars, and turn into spendable money within a few business days. A high-yield savings account and a Treasury bill look nearly interchangeable on a rate-comparison page. The decision between them is rarely won on the headline number, though. It is won on a single line that most bank marketing never mentions: a Treasury bill’s interest is exempt from state and local income tax, and a savings account’s interest is not.

For a saver in Texas or Florida, that line is worth exactly nothing, and the choice comes down to whichever pays the higher rate this week. For a saver in California or New York, the same line can flip the ranking entirely, turning a slightly lower headline yield into the better take-home return. This is the binary version of the question. (For the three-way comparison that adds money market funds to the mix, see T-bills vs HYSA vs money market funds — this piece stays narrowly on the head-to-head where the real decision lives.)

For a saver in a no-income-tax state, pick whichever pays more this week — in early June 2026 that was the high-yield savings account, at roughly 4.0% to 4.2% APY versus about 3.72% on the 3-month Treasury bill. For a saver in a high-tax state, run the after-tax math: because none of a T-bill’s interest is taxed by the state, the bill can deliver the higher take-home yield even when its headline rate is lower. The savings account also wins on liquidity and simplicity; the Treasury bill wins on the tax exemption and the absence of any $250,000 insurance ceiling.

The one difference that usually decides it: state taxes

Interest from a high-yield savings account is ordinary income at every level. The federal government taxes it at your marginal rate, and so does your state, if your state has an income tax. Interest from a US Treasury bill is also ordinary income federally, but it is exempt from all state and local income taxes — a structural feature of federal law, not a promotional gimmick, and one the Treasury itself confirms in its tax guidance. The Internal Revenue Service treats the federal portion identically for both instruments; the divergence is entirely at the state line.

How much that exemption is worth depends on where you live. In the nine states with no broad income tax on wages and interest — Texas, Florida, Washington, Nevada, Tennessee, Wyoming, Alaska, South Dakota, and New Hampshire — it is worth zero, and the comparison collapses to a plain rate contest. In a high-tax state, it is worth real money. California’s top marginal rates run to 13.3%, with most working households landing in brackets around 9.3%. New York City residents stack a city income tax on top of the state’s. For those savers, every dollar of T-bill interest arrives untaxed by the state, while every dollar of savings interest gives some back.

One practical warning that trips up first-time T-bill buyers. A brokerage 1099 form does not always flag the state exemption for you automatically, so the exemption sometimes has to be claimed by hand as an adjustment on the state return. The money is exempt either way; you just have to make sure your tax software or preparer actually subtracts it.

A worked example: $25,000 for a California household

Numbers make the abstraction concrete. Take a California household in the 9.3% state marginal bracket holding $25,000, and use the early-June-2026 rates: 4.10% on a top high-yield savings account, 3.72% on a 3-month Treasury bill. To keep the comparison clean, this looks only at the state-tax layer, since the federal tax is identical on both and washes out.

• High-yield savings at 4.10%. Interest of about $1,025. California takes 9.3% of it, or roughly $95. Take-home interest is about $930, an after-state-tax yield of 3.72%.
• 3-month Treasury bill at 3.72%. Interest of about $930. California takes nothing. Take-home interest is about $930, an after-state-tax yield of 3.72%.

At these specific rates the two land in a near-tie for the California saver — the savings account’s 38-basis-point headline lead is almost exactly cancelled by the state tax it pays and the T-bill avoids. That is the whole point. A spread that looks decisive on a comparison page evaporates once the state tax is netted out. Shift the inputs even slightly toward the saver’s high-tax disadvantage — a 13.3% bracket, or a moment when the T-bill yield closes the gap with savings — and the Treasury bill pulls clearly ahead. Run the same example for a Texas saver, where the state rate is zero, and the savings account keeps its full 4.10% lead. Same two products, opposite answers, decided by a zip code.

The rule that falls out of this: never compare the headline APY against the headline bill yield. Convert the T-bill’s tax-free yield into its taxable-equivalent — divide it by one minus your state marginal rate — and compare that to the savings APY. For the 9.3% California saver, a 3.72% tax-free T-bill is equivalent to a roughly 4.10% taxable savings rate. For the 13.3% saver, it is equivalent to about 4.29%.

Liquidity: immediate versus wait-or-sell

This is where the savings account earns its keep. The money in a high-yield savings account is reachable on a 1-to-3-business-day ACH transfer to your checking account, at the rate the bank is currently paying, with no penalty and no market risk. That makes it the natural home for an emergency fund — the cash you might need on short notice and cannot afford to see drop in value.

A Treasury bill is liquid on a different and slower schedule. Held to maturity — 4, 8, 13, 17, 26, or 52 weeks depending on the bill — it pays its stated yield in full and the cash settles to your linked account. Needed before maturity, it has to be sold on the secondary market through a brokerage, at a price that moves inversely with interest rates. Sell when rates have risen since you bought, and you take a small loss on principal; sell when rates have fallen, and you may pocket a small gain. Either way the guaranteed yield only holds to maturity. The standard fix is a ladder — staggering bills so one matures every few weeks — which restores rolling access without selling early. The mechanics of buying, laddering, and auto-rolling on the government’s own platform are covered in how to buy Treasuries on TreasuryDirect.

The honest framing: a savings account is liquid by design, a T-bill is liquid by sale. For the slice of cash you genuinely might need next week, that difference outweighs any tax edge.

The guarantees: FDIC $250k versus full faith and credit

Both instruments sit at the safe end of the spectrum, but the safety is constructed differently, and the difference only matters at scale.

A high-yield savings account is protected by the Federal Deposit Insurance Corporation up to $250,000 per depositor, per insured bank, per ownership category. The per-category detail is more generous than it first sounds: an individual account, a joint account, and certain trust accounts at the same bank are insured separately, so a couple can cover well past $250,000 at a single institution by structuring ownership, or simply by spreading deposits across multiple FDIC-insured banks. Within those limits the FDIC’s record is perfect — it has covered 100% of insured deposits in every bank failure since 1933.

A Treasury bill carries no insurance because it needs none. It is a direct obligation of the US Treasury, backed by the full faith and credit of the federal government, with no $250,000 ceiling and no bank sitting between you and the issuer. For a saver holding more than the FDIC limit, that is a genuine structural advantage: a $400,000 cash position fits in T-bills without splitting it across banks or juggling ownership categories. Below the insurance limit, the two guarantees are equivalent in any practical sense — both pay out in full, by different plumbing.

Putting it together: who should pick which

The decision rule is short once the pieces are on the table.

Choose the high-yield savings account when you live in a no-income-tax or low-tax state, the balance is comfortably under the FDIC limit, and you value immediate, penalty-free access — which describes most households’ emergency funds and first cash tier. It is the simpler product: one linked account, one 1099-INT at year-end, rates that move within days of any Federal Reserve rate change, and nothing to administer. If you want the mechanics of the account type itself, the HYSA glossary entry covers how online banks fund the higher rate.

Choose the Treasury bill when you live in a high-tax state and the state exemption tips the after-tax math its way, when your balance exceeds the FDIC limit and you would rather not split it across banks, or when you can hold to maturity and want a yield locked at purchase rather than a savings rate the bank can cut at will. High-net-worth savers in California and New York frequently make T-bills their primary cash vehicle for exactly the tax reason worked through above.

For many households the answer is both: a high-yield savings account for the immediately-needed tier, and a short T-bill ladder for the larger, less-urgent balance where the tax exemption and the locked yield start to pay off. The broader map of where each cash tier belongs is in where your dollars actually earn. Whatever the split, the discipline is the same one bank marketing keeps quiet about: compare the after-tax yield, and let your state — not the headline rate — cast the deciding vote.

Sources

• State and local tax exemption on Treasury interest, and federal taxability: TreasuryDirect — Tax Forms and Withholding and IRS — Topic No. 403, Interest Received.
• 3-month Treasury bill yield (~3.72% as of June 5, 2026): U.S. Department of the Treasury — Daily Treasury Bill Rates and FRED — 3-Month Treasury Bill Secondary Market Rate (DTB3).
• High-yield savings account rates (~4.0%–4.2% APY no-strings; promotional rates up to 5.00% with caps/conditions; FDIC national average 0.38%) as of June 2026: Bankrate — Best High-Yield Savings Accounts and NerdWallet — Best High-Yield Savings Accounts.
• FDIC $250,000 per depositor, per bank, per ownership category: FDIC — Understanding Deposit Insurance and FDIC — Deposit Insurance FAQs.

Rates on this page reflect early June 2026 and move with the front end of the Treasury curve; if a figure looks stale against current conditions, the Treasury and rate-tracking sources above update daily, and you can flag it via contact so we reconcile it.