T-Bill Ladder vs. HYSA in 2026: When State Tax Flips the Math

What remains is not yield but friction. A ladder of bills — one of exactly four marketable Treasury security types, alongside notes, bonds, and TIPS — is bought through Federal Reserve Bank of New York auctions and traded in secondary markets, yet it still asks a few more clicks than a banking app. Those clicks feel heavier than they are; measured in dollars, the switch pays for itself in the first year.

One sentence of the United States Code does more damage to the advertised-APY leaderboard than any rate war: 31 U.S.C. §3124(a) bars states and localities from taxing interest on direct obligations of the United States. Buy a 4-week or 26-week bill through TreasuryDirect or any brokerage and the accreted discount lands on Form 1099-INT, Box 3 — federally taxable, then subtracted as a U.S.-government-interest adjustment on the state return (the mechanic behind California's Schedule CA (540)). Interest from a Marcus or Ally savings account travels the opposite path: ordinary income, taxed by Sacramento and Washington simultaneously. Rate-ranking apps compare those two streams pre-tax, as if the second column didn't exist — a pure salience failure, where the interface shows the number the bank markets and hides the number the state legislature taxes. The highest advertised APY does not automatically win, because the bill's yield arrives pre-state-tax and the bank's arrives fully loaded.

Because both instruments face the same federal marginal rate, the federal layer cancels and the ranking collapses to one expression: tax-equivalent yield equals the T-bill yield divided by (1 − your state rate). Take the 9.3% case: a 3.85% bill carries a TEY of 3.85 ÷ 0.907 = 4.24%, so the competing bank must pay roughly 39 basis points extra purely as compensation for the state tax its interest incurs. The formula is trivial; the friction is that no dashboard computes it for you. The full state-by-state grid built from this expression belongs to the Break-Even Table, so I won't rebuild it here.

The §3124 Wedge

The standard objection is liquidity, and the ladder answers it mechanically rather than rhetorically. Split the emergency fund across the six bill tenors — 4, 8, 13, 17, 26, and 52 weeks, the 17-week having been introduced in October 2022 — and stagger purchases so a rung matures every few weeks. The "locked" instrument becomes a rolling paycheck of principal: each maturing rung is either spent or re-bid at the next auction conducted by the Federal Reserve Bank of New York. Bills are also marketable securities, so a rung can be sold in the secondary market if a genuine emergency outruns the schedule — at a price that varies with prevailing rates, which is the honest cost of early exit.

Compress everything into the number that decides the race: state-tax drag ≈ state rate × HYSA yield. On a 4.00% HYSA, California's 13.3% top rate imposes roughly 53 basis points of drag — the bank's headline premium must exceed that just to reach parity. Against the thin premiums banks currently pay over matching-maturity bills, the bill column wins on after-tax yield in every state clearing the ~4% threshold this guide sets; the bank column wins only on instant withdrawal, which the ladder approximates. The action step is free: pull your last state return, read off your marginal rate, multiply it by the best HYSA yield offered, and compare that product to the bill spread before the next 4-week auction closes — then re-run it quarterly, because both sides move.

Series DTB3 on FRED — the St. Louis Fed's feed of the Treasury's Daily Treasury Par Yield Curve Rates — is the source of record for the front end, and after the Fed's late-2025 cuts it has printed inside a rough 3.6-to-3.9-percent band. Two housekeeping rules follow. First, refresh that print on publication day: the three-month bill reprices at every weekly auction, so a yield pulled from last month's screenshot is stale data wearing a current timestamp. Second, treat DTB3 as the fixed leg of the comparison; everything else on the board is measured against it.

The bank side needs two anchors, not twenty. According to the FDIC's National Rate and Rate Cap Report, the national savings average sits near 0.45 percent — more than 300 basis points below bills, which makes the branch account a control group, not a contender. At the other pole, Bankrate's weekly expert survey tracks the online top tier — Marcus, Ally, Barclays and peers — printing roughly 3.9 to 4.1 percent. Set the poles side by side and the finding is structural: competitive HYSAs cluster within about ±30 basis points of T-bill yields in 2026. That tightness is precisely why the advertised-APY leaderboard fails. It ranks pre-tax digits whose premium over bills is often thinner than the state-tax drag it refuses to model — a textbook salience artifact, sorting on the number that is visible rather than the number you keep.

Who does the §3124 exemption covered above actually reach? Per the Tax Foundation, 41 states plus D.C. levy broad wage income taxes, while nine states — concentrated in the Sun Belt and the Plains — levy none, and New Hampshire fully repealed its interest-and-dividends tax effective January 1, 2025. Read that as coverage, not trivia: for the large majority of savers the wedge is live, and the pre-tax leaderboard answers a question they stopped needing asked. Only in the nine non-taxing states does the comparison collapse to raw yield and convenience — the sole constituency a HYSA's convenience premium can legitimately court.

The 2026 Yield Board: FRED's 3.6

History sets the prior. Comparing the FRED archive against Bankrate's rate archive across 2023–2025: during the hiking phase, top online HYSAs trailed three-month bills by roughly 20 to 80 basis points; once cuts began, the gap compressed to roughly 10 to 30. Neither regime ever paid the bank a premium. In 2026 the burden of proof sits with whichever institution advertises one.

On this board as printed, the bill column wins for everyone in the taxing jurisdictions mapped above; the bank column competes only where no wedge exists. Publication-day action: pull DTB3, pull the top of the Bankrate tier, run the tax-equivalent division prescribed earlier in this guide, and re-run it quarterly — if the advertised premium does not clear your state's drag, the ladder holds the emergency fund until the next auction cycle says otherwise.

Rate-ranking apps have a blind spot shaped like Sacramento. Every leaderboard sorts by advertised APY — a pre-tax number — which quietly assumes you live where interest goes untaxed. The moment your state levies income tax on deposit earnings, the printed APY is the wrong sort key, and the top result on the screen is often the worst after-tax deal on it. Anyone who builds comparison interfaces knows the sort key is the product; here, the industry sorts by the variable that flatters the advertiser.

The fix compresses the entire debate into one subtraction. Compute the state-tax hurdle: state rate × HYSA APY. At a 5% state rate and a 4.00% APY, the hurdle is 20 bps. The HYSA wins only if its APY exceeds the best matching-maturity T-bill by MORE than that hurdle — one subtraction replaces the whole argument. Notably, this arithmetic appears nowhere in the standard comparison flow: no aggregator surfaces a break-even threshold, no bank disclosure computes one. The single number that settles the debate is the number the category leaves out.

Two refinements before trusting the quick hurdle. First, the exact break-even premium is the bill yield × s/(1−s), not s × APY — the forgone base is the bill, so the true bar runs a touch above the shortcut at high rates: California's real bar is ~39 bps against the quick 37, New York City's ~46 against 43. Second, Illinois is where the thesis's rough 4% line gets drawn — its hurdle exactly consumes the ceiling premium — and Colorado sits close enough behind it that the quarterly re-run, not this table, decides them.

Score liquidity instead of hand-waving it. Award the HYSA one point for instant withdrawal. Award the ladder one point for the weekly-maturing rung plus same-day ACH from brokerage settlement — a laddered book matures something every week, and settlement reaches your bank the day you pull it. The residual gap is timing risk measured in days, and for households whose emergency drawdowns arrive on monthly, not daily, timescales it is worth no more than 10 bps — an order of magnitude below every hurdle in the table except Pennsylvania's, and the only force that can plausibly flip Colorado, and only within a couple of basis points.

The Break-Even Table

Safety is a tiebreaker, not a criterion. Below the deposit-insurance ceiling, both wrappers are effectively default-risk-free, so the verdict is decided purely on after-tax yield. Above that ceiling the analysis ends: Treasury backing is uncapped, deposit insurance is not, and the ladder wins by default in every state — including the nine that levy no income tax at all.

Run the subtraction tonight: your state rate × your APY, set against your APY minus the best matching-maturity bill. Then make the re-run a recurring calendar event — early April 2026, when Q1 statements post — because the post-cut convergence that compressed the premium is precisely the input most likely to move. Friction, not ignorance, is why people never recompute; automate the trigger and the framework runs itself.

The cleanest comparison in this guide carries an asterisk no leaderboard prints: every tax-equivalent calculation above assumes you get to choose when the emergency arrives. An emergency fund exists precisely because you don't. The bill yield is a hold-to-maturity number; to collect it, each bill must survive to its auction date. Sell into a rising-rate week because the water heater failed, and the mark-to-market haircut comes out of principal — landing, by construction, in the worst week of your financial year. At the front end of the curve those haircuts are typically small, but they are not zero, and they strike exactly the margin the ladder was built to protect.

That is the first limitation of the evidence itself. The convergence documented on the yield board is a snapshot of a short post-cut window, and deposit repricing has never been symmetric across cycles — banks tend to pass funding-cost cuts through faster than hikes, so the deposit-versus-bill spread can reopen without anything "breaking." A few quarters of prints is a weather report, not a climate model. The honest reading is that the data strongly supports the process — run the division, re-run it quarterly — more than any permanent ranking. Treat the current answer as this quarter's answer, not a constitution.

Variance across cases runs along three axes the aggregates flatten. Product: the statutory exemption covered at the top of this guide attaches cleanly to direct Treasury obligations, but a Treasury money-market fund inherits it only proportionally in many states — scaled to the fund's certified share of government obligations and subject to each state's own threshold test — so two savers holding "Treasuries" can face different after-tax outcomes. Person: the rate that matters is your marginal rate on interest income, not your headline bracket; a large fund in a graduated-rate state, or a mid-year move across state lines, can shift that marginal rate underneath you. Balance: per-trade costs and bid-ask spreads are roughly fixed per transaction, so they consume a visibly larger share of the wedge on a small ladder than a large one — read your broker's schedule before assuming the arithmetic transfers.

When does the rule actually break? Narrower than the caveats imply, but real. A promotional savings premium is justified only when the extra yield, net of your state's tax drag, outearns the matching bill over the full window you will realistically keep the account open — teasers decay, and the bonus is paid once. In states that levy no income tax, the formula collapses to a nominal comparison and convenience legitimately decides; the rule doesn't fail there, it stops being decisive. And the forced-sale path risk is the one scenario where the ladder can lose money the savings account cannot.

What the Data Doesn't Tell You

One myth deserves burial here because it survives expertise: the belief that the highest advertised APY automatically wins fails least among novices and most among readers who already know the tax math — the app sorts by that number by default, and defaults beat intentions. The fix is procedural, not intellectual. Calendar the recomputation beside an obligation you cannot skip, and each quarter pull three inputs: your state's current marginal rate on interest income from the revenue department's official schedule, the matching-maturity print from Treasury's daily par-yield release, and your HYSA's stated rate net of any expired teaser. Three verified numbers, one division, done.

TreasuryDirect has no auto-roll. That single missing feature — not any flaw in the tax-equivalent formula — is where most ladders actually die, and it heads a short list of failure modes the spread itself conceals. Four erode the bill ladder's edge at the margins; a fifth suggests the binary was never complete.

Start with the path rates take. CME FedWatch pricing points to additional Fed cuts through 2026, and each cut reprices a rolled rung within weeks, because auction results track the policy rate almost immediately. Banks behave differently: they have historically trimmed savings APYs with a one-to-three-month lag. In a falling-rate year, that lag flips the ordering for a quarter or two — a sluggish HYSA can out-earn an actively rolled ladder before the exemption reasserts itself. The decision rule is correct at every re-run date and can still lose in between them.

Second, exit risk. A savings account redeems at par, always. A bill sold early embeds rate risk instead: a 26-week issue carries duration of roughly 0.48 years, so a 100-basis-point rise inflicts about a half-percent price hit. Marketable bills trade — unlike the non-marketable savings bonds the Treasury issues directly to individuals — and tradability is exactly what exposes you to markdowns. The ladder is only as liquid as your maturity calendar: match rungs to known expenses or accept the price risk explicitly.

Third, the failure mode my subfield exists to study. Madrian and Shea's 2001 auto-enrollment finding and Thaler and Benartzi's Save More Tomorrow results both show that outcomes track whichever path demands the least action. TreasuryDirect demands the most — manual reinvestment of every maturing rung. One forgotten rollover parks proceeds at zero percent, and weeks of idling can consume most of that rung's annual pickup. The edge decays not through bad math but through unexecuted clicks.

What the Spread Hides

Fifth, the suppressed third option. For top-bracket Californians, Vanguard's municipal money funds rewrite the answer: VMSXX holds federally tax-exempt paper, the California-specific VCTXX adds state exemption, and 7-day yields have run around 3% in recent prints. After tax, either fund can net more than both the HYSA and the ladder. The advertised-APY leaderboard cannot see them, because munis compete on after-tax income — the highest-headline-rate-wins belief fails a second time here.

Sixth, shelf life. The verdict rests on a gap of thirty basis points or fewer between two independently moving yields; a promotional HYSA boost or one strong auction day can invert any row of the break-even table within a month. Two calendar entries neutralize most of this: a recurring reminder synced to your earliest rung's maturity, and a quarterly appointment to redo the division. Check the table's last row first if you file in California.

Hold the verdict loosely, because it stands on a knife edge. If the HYSA premium widens past roughly 20 bps — say the bank pays 4.10% against the 3.80% ladder — Boston flips back to the bank; at these inputs the hurdle is 20.5 bps. That margin sits well inside a normal quarter of deposit-rate churn, so treat the answer as perishable: re-run the tax-equivalent calculation quarterly and hold whichever instrument currently wins, the standing discipline the guide's final rules codify.

The tax code and the yield board have already decided the 2026 cash question; the five rules below decide whether you actually collect the answer. They are built as standing infrastructure — one screen, one carve-out, one architecture, one buffer, one calendar trigger — because in behavioral terms the enemy is not ignorance of the formula but the small recurring frictions that let a fully understood arbitrage sit unexecuted. Run them in order.

Rule 1 — the TEY screen. Before moving a dollar, compute tax-equivalent yield — the T-bill yield divided by (1 minus your state income-tax rate) — and compare it straight to your HYSA's APY; buy whichever number is higher. A saver facing a 6.5% state rate divides a 3.80% bill yield by 0.935 and gets 4.06%, which beats a 4.00% HYSA even though the bill's sticker sits twenty basis points lower. One division retires the leaderboard habit: the contest is between two adjusted numbers, never between two advertisements.

Rule 2 — the no-tax-state carve-out. File in Alaska, Florida, Nevada, New Hampshire, South Dakota, Tennessee, Texas, Washington, or Wyoming and the §3124 wedge shields interest you were never going to owe tax on — the benefit collapses to zero. There the default flips: hold the HYSA unless bills out-yield it outright by at least 10 basis points, a margin that pays you for accepting ladder complexity. For these residents the advertised APY is nearly the whole story — the narrow exception that proves the rule.

Rule 3 — the rung architecture. Split the laddered balance into six equal rungs and buy 4-, 8-, 13-, 17-, 26-, and 52-week bills, so roughly one rung matures every four weeks and the fund approaches full liquidity within a quarter. Enable auto-roll at Fidelity or Schwab, and never hold emergency money in plain TreasuryDirect: as covered above, its missing auto-roll turns every rollover into a manual event, and each manual event is a fresh opening for procrastination to compound into idle cash. The governing principle is the one behind every automation that survives contact with real life — move the default, not the intention.

Boston vs. Austin

Rule 4 — the two-tier buffer. Keep one month of essential expenses in the HYSA as the instant-access tier and ladder everything above it. The after-tax edge is earned over holding periods, and money you may need this month has no holding period — it needs same-day availability more than it needs the incremental yield on a slice of the balance. The buffer also protects the ladder itself: tapping a rung mid-cycle forces an unplanned secondary-market sale.

Rule 5 — the quarterly re-underwrite. After each Fed decision or quarter-end, recompute the hurdle — your state rate multiplied by your HYSA's APY — against the live spread between that APY and the matching-maturity bill yield. If the spread exceeds the hurdle, migrate the ladder back to the bank. The mechanics cut both ways: a bank raising its APY raises your hurdle, while rate cuts passing through to bills faster than to deposits widen the spread. The 2026 answer is a standing calculation, not a one-time verdict.

The sweep takes one afternoon to build and minutes, not hours, to maintain each quarter. Set the calendar entry now: the morning after the next FOMC decision, re-run Rule 1 with that week's bill print and your bank's current APY, and let whichever instrument wins hold the money until the next trigger fires.

The paperwork behind those numbers is trivial in both directions. The Texan receives one 1099-INT, transcribes one figure onto the federal return, and is done — no state return exists to reconcile. The Bostonian takes the identical federal step, then carves the ladder's Box 3 Treasury interest out on Schedule B of Massachusetts Form 1, the interest-and-dividends schedule where U.S. obligations come off before the state computes taxable interest. Call it a five-minute annual task — the ladder's entire administrative cost — and price it honestly: against the $29-to-$120 annual stakes in play, five minutes works out to an effective hourly rate in the hundreds, exactly the trade-off that friction-heavy money apps bury.

Compress the pair into an identity and the driver is unmistakable: the $120/year swing between the two cities equals exactly the 5% state rate × 4.00% yield × $60,000. The state can tax only the bank leg — §3124 walls off the ladder leg completely — so every point of state rate transfers dollar-for-dollar out of the HYSA column. Geography, not rate-shopping skill, decides the winner at 2026 spreads; shaving hundredths off the bank's APY cannot offset a full state-tax drag, but your filing address does that work automatically.

Hold the verdict loosely, because it stands on a knife edge. If the HYSA premium widens past roughly 20 bps — say the bank pays 4.10% against the 3.80% ladder — Boston flips back to the bank; at these inputs the hurdle is 20.5 bps. That margin sits well inside a normal quarter of deposit-rate churn, so treat the answer as perishable: re-run the tax-equivalent calculation quarterly and hold whichever instrument currently wins, the standing discipline the guide's final rules codify.

Five Rules for the 2026 Cash Sweep

The tax code and the yield board have already decided the 2026 cash question; the five rules below decide whether you actually collect the answer. They are built as standing infrastructure — one screen, one carve-out, one architecture, one buffer, one calendar trigger — because in behavioral terms the enemy is not ignorance of the formula but the small recurring frictions that let a fully understood arbitrage sit unexecuted. Run them in order.

Rule 1 — the TEY screen. Before moving a dollar, compute tax-equivalent yield — the T-bill yield divided by (1 minus your state income-tax rate) — and compare it straight to your HYSA's APY; buy whichever number is higher. A saver facing a 6.5% state rate divides a 3.80% bill yield by 0.935 and gets 4.06%, which beats a 4.00% HYSA even though the bill's sticker sits twenty basis points lower. One division retires the leaderboard habit: the contest is between two adjusted numbers, never between two advertisements.

Rule 2 — the no-tax-state carve-out. File in Alaska, Florida, Nevada, New Hampshire, South Dakota, Tennessee, Texas, Washington, or Wyoming and the §3124 wedge shields interest you were never going to owe tax on — the benefit collapses to zero. There the default flips: hold the HYSA unless bills out-yield it outright by at least 10 basis points, a margin that pays you for accepting ladder complexity. For these residents the advertised APY is nearly the whole story — the narrow exception that proves the rule.

Rule 3 — the rung architecture. Split the laddered balance into six equal rungs and buy 4-, 8-, 13-, 17-, 26-, and 52-week bills, so roughly one rung matures every four weeks and the fund approaches full liquidity within a quarter. Enable auto-roll at Fidelity or Schwab, and never hold emergency money in plain TreasuryDirect: as covered above, its missing auto-roll turns every rollover into a manual event, and each manual event is a fresh opening for procrastination to compound into idle cash. The governing principle is the one behind every automation that survives contact with real life — move the default, not the intention.

Rule 4 — the two-tier buffer. Keep one month of essential expenses in the HYSA as the instant-access tier and ladder everything above it. The after-tax edge is earned over holding periods, and money you may need this month has no holding period — it needs same-day availability more than it needs the incremental yield on a slice of the balance. The buffer also protects the ladder itself: tapping a rung mid-cycle forces an unplanned secondary-market sale.

Rule 5 — the quarterly re-underwrite. After each Fed decision or quarter-end, recompute the hurdle — your state rate multiplied by your HYSA's APY — against the live spread between that APY and the matching-maturity bill yield. If the spread exceeds the hurdle, migrate the ladder back to the bank. The mechanics cut both ways: a bank raising its APY raises your hurdle, while rate cuts passing through to bills faster than to deposits widen the spread. The 2026 answer is a standing calculation, not a one-time verdict.

The sweep takes one afternoon to build and minutes, not hours, to maintain each quarter. Set the calendar entry now: the morning after the next FOMC decision, re-run Rule 1 with that week's bill print and your bank's current APY, and let whichever instrument wins hold the money until the next trigger fires.

What to do next

Frequently Asked Questions

Why isn't the interest on my Treasury bills taxed by my state the way my savings-account interest is?

31 U.S.C. §3124(a) bars states and localities from taxing interest on direct obligations of the United States, so the bill's accreted discount lands federally taxable on Form 1099-INT Box 3 and is then subtracted as a U.S.-government-interest adjustment on the state return — the mechanic behind California's Schedule CA (540).

How much higher does an online bank's APY have to be before it beats a 3.85% T-bill in a 9.3% state?

Roughly 39 basis points, because the tax-equivalent yield formula (bill yield divided by 1 minus your state rate) puts the break-even at 3.85 ÷ 0.907 = 4.24%.

How much does it actually cost me each year to leave my emergency fund in the HYSA instead?

On a $50,000 emergency fund the error runs about $111 a year, since the 4.00% HYSA is taxed down to 3.63% while the 3.85% T-bill arrives untaxed at the state level.

What happens if I need cash before the next rung of my bill ladder matures?

Bills are marketable securities, so a rung can be sold in the secondary market if a genuine emergency outruns the schedule — at a price that varies with prevailing rates, which is the honest cost of early exit.

Does any of this matter if I live in a state with no income tax?

Per the Tax Foundation, 41 states plus D.C. levy broad wage income taxes while nine states levy none, and New Hampshire fully repealed its interest-and-dividends tax effective January 1, 2025 — so only in those nine non-taxing states does the comparison collapse to raw yield and convenience.

Aren't T-bills riskier than my savings account since they aren't FDIC insured?

T-bills are backed by the full faith and credit of the United States with no dollar cap, whereas FDIC insurance on the HYSA covers just $250,000 per depositor, per bank.

Quick answers

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