High-yield savings vs a 4-week T-bill for your emergency fund: which earns more after tax?

If you keep an emergency fund, two parking spots come up again and again: a high-yield savings account (HYSA) and a short-term Treasury bill. They look interchangeable — both about as safe as cash gets, with headline rates that land in the same neighborhood. What makes this an actual decision is tax: a 4-week T-bill and a HYSA can advertise the same rate and still leave you with different amounts of money, because they're taxed differently. This article runs the honest, illustrative after-tax math, then explains why — for an emergency fund specifically — liquidity often tips the answer back toward a savings account.

The two HYSAs people most often weigh for this job are Ally Bank's Online Savings Account and Barclays' Tiered Online Savings — both no-minimum, no-monthly-fee, FDIC-insured accounts. The T-bill is a benchmark, not something we earn anything on; you'd buy it yourself at TreasuryDirect or through a brokerage.

Disclosure & not-advice note: YieldPerch earns a commission when you open an account through some of our links via Commission Junction, at no extra cost to you. This never changes which accounts we cover, how we rank them, or the rates shown. The T-bill is included as a non-affiliate benchmark only. All APYs and dollar figures below are illustrative, change frequently, and were last reviewed in 2026 — verify the current rate on each provider's official site before you act. This is general information, not financial advice.

The one tax fact this whole comparison rides on

• Treasury bill interest is exempt from state and local income tax — but fully subject to federal income tax. T-bills are not federally tax-advantaged; the only break is at the state level.
• HYSA interest is fully taxable — federal and state. Your bank reports it on a 1099-INT and it's taxed as ordinary income.

So the T-bill's entire edge is one thing — skipping state and local tax — and it has a calculable size:

At roughly equal headline rates, a T-bill's after-tax advantage over a HYSA is approximately headline rate × your state marginal income-tax rate.

Say both pay around 4.0% (illustrative — real short-term rates drift) and you're in a state with a 6% marginal rate. The T-bill's state-tax savings ≈ 4.0% × 6% ≈ 0.24 percentage points, so it behaves like a ~4.24% account after state tax while the HYSA stays at ~4.0%. On a $20,000 fund held a year, that's roughly $48 of difference — a real wedge, but small.

The caveat that flips the answer for millions of savers

If you live in a state with no income tax — Texas, Florida, Washington, Tennessee, Nevada, South Dakota, Wyoming, Alaska, and (for wage/interest income) New Hampshire — the T-bill's state-tax exemption is worth exactly zero. At equal headline rates a T-bill and a HYSA are a wash before you even factor in liquidity, and the more flexible HYSA wins on convenience. The "which earns more after tax" question simply has a different answer depending on where you file.

Side-by-side: Ally HYSA vs Barclays HYSA vs a 4-week T-bill

Each HYSA offer is compared individually against a 4-week (one-month) Treasury bill. The yield column is illustrative — verify the live numbers before deciding.

Check current options: Ally Bank Online Savings Account - Barclays Tiered Online Savings

Rates are illustrative and change frequently — verify the current APY and the latest 4-week T-bill auction rate on the official sites before opening anything. YieldPerch earns nothing on T-bills, which you buy at TreasuryDirect or through a broker.

Why liquidity usually tips an emergency fund toward the HYSA

The after-tax math can favor the T-bill in a high-tax state — but an emergency fund has a job most other money doesn't: it has to be available the day the emergency happens. That's where the T-bill's structure works against it.

• A 4-week bill locks your cash until maturity. If your transmission dies in week two, you don't get the money on demand — you wait out the term or sell on the secondary market through a broker, which means a trade, a spread, and a next-business-day settlement. Doable, but friction at the exact moment you want none.
• A HYSA is built for instant access. With Ally or Barclays you transfer to linked checking and the money is generally available same- or next-day, no trade and no maturity to wait on. Based on published terms, both treat savings as everyday-liquid cash.
• The give-up is small; the convenience is large. That wedge — about $48 a year on $20k in a 6%-tax state, $0 in a no-tax state — is a modest price for cash that's genuinely on call.

A common middle path: keep one-to-two months of expenses in a HYSA for instant access, and ladder the deeper, rarely-touched layer into short T-bills to capture the state-tax break while staying within a week of cash. That's a structure, not a recommendation — and only where the exemption is worth something.

Ally vs Barclays: which HYSA is the better liquid anchor?

If the liquid layer belongs in a HYSA — the common call for a true emergency fund — the choice between the two offers comes down to feel, not a meaningful rate gap:

• Ally Online Savings pairs a flat APY across balances with deep tooling — buckets (named sub-accounts inside one account, so "emergency fund," "car repair," and "insurance deductible" live separately) plus round-ups and automated transfers. Based on published features, it's the stronger pick if you want to organize and automate the fund.
• Barclays Tiered Online Savings keeps things deliberately simple — one balance, no buckets, a tiered APY where the posted rate can vary by balance band. It suits savers who'd rather see a single number. Confirm which tier your balance actually lands in before assuming the top rate.

Both are no-minimum, no-fee, and FDIC-insured. The rate difference at any moment is usually small — let the feature fit and the current posted APY break the tie.

The decision rule

Stripped down to what actually matters:

1. No-income-tax state? The T-bill's advantage is zero. Use a HYSA — a wash on yield, a win on liquidity.
2. High-tax state, cash that's genuinely "set and forget"? A short T-bill (or a weekly ladder) can edge out the HYSA after state tax — by a small margin, if you're comfortable with maturities and occasional secondary-market sales.
3. A real emergency fund you might need any day? Liquidity usually wins — keep your front-line cushion in a HYSA like Ally or Barclays, and ladder only the deeper layer.

There's no universal winner here, only a fit. Run your own numbers with your state's marginal rate and the live rates of the day, and let your situation pick.

Frequently Asked Questions

Do you pay state tax on a high-yield savings account but not a T-bill?

Yes — that's the core difference. HYSA interest is fully taxable at both the federal and state level and shows up on a 1099-INT as ordinary income. Treasury bill interest is exempt from state and local income tax but is still fully subject to federal income tax. So the T-bill's only tax advantage is skipping state and local tax — which is worth nothing in a state with no income tax. Figures here are illustrative; this is general information, not financial advice.

At the same rate, does a 4-week T-bill really earn more than a HYSA?

Only after tax, and only in a state with income tax. At roughly equal headline rates, the T-bill's after-tax edge is approximately your headline rate multiplied by your state marginal tax rate — for example, about 0.24 percentage points at a 4% rate in a 6%-tax state. That's a small, real wedge. In a no-income-tax state the two are a wash before liquidity, which then favors the HYSA. Verify current rates before deciding.

Can I get my money out of a 4-week T-bill early if I have an emergency?

Not on demand. A 4-week bill returns your principal plus interest at maturity (about four weeks out). If you need the cash sooner, you'd sell the bill on the secondary market through a brokerage, which involves a trade, a bid/ask spread, and a next-business-day settlement. By contrast, a HYSA like Ally or Barclays lets you transfer to checking with same- or next-day access and no trade — which is exactly why many savers keep their front-line emergency cash in a HYSA.

Is a HYSA or a T-bill safer for emergency savings?

Both are considered very safe. HYSAs at banks like Ally and Barclays are FDIC-insured up to coverage limits, and Treasury bills are backed by the full faith and credit of the U.S. government. For most savers the safety difference is negligible; the practical decision comes down to after-tax yield (which depends on your state) and how quickly you need access to the cash. This is general information, not financial advice — confirm coverage details and current rates on the official sites.

Where do I actually buy a 4-week T-bill?

Directly from the U.S. Treasury at TreasuryDirect, or through most brokerage accounts (often via the new-issue auction or the secondary market). There's no affiliate involved — YieldPerch earns nothing on Treasury purchases. If you prefer a single liquid account instead, the HYSAs compared above are opened online directly with the bank. Always verify the latest auction rate and the current HYSA APY before committing.

Rates change, figures are illustrative. All APYs, the T-bill rate, and dollar amounts here are illustrative, last reviewed in 2026 — not live quotes. Verify the current HYSA APY on each bank's official site and the latest 4-week T-bill auction rate at TreasuryDirect before opening or buying anything. This is general information about deposit and Treasury products — not financial, tax, or investment advice.