Your High-Yield Savings Account Is Quietly Losing to a 4-Week T-Bill

Real question: if you live in New York, California, or any state with a real income tax — why is your emergency fund in a high-yield savings account?

Most personal-finance advice treats high-yield savings as the obvious answer for cash. It used to be. In a 2026 rate environment, with state income tax in the picture, the math has quietly flipped. The Treasury is paying more than your bank on an after-tax basis — for a product the IRS literally exempts from state and local tax.

It’s called a Treasury bill. Specifically, a 4-week T-bill. And in high-tax states, it has become the highest-yielding place to park cash, full stop.

How T-Bills actually work

A T-bill is a short-term loan to the U.S. Treasury. You buy it at a discount; it matures in 4, 8, 13, 17, 26, or 52 weeks at face value. The difference is your interest.

Buy a $10,000 4-week T-bill at $9,972. Four weeks later, the Treasury wires you $10,000. You earned $28 of interest, which annualizes to roughly 3.61% — the current 4-week yield as of June 2026.

Three things are unique compared to your savings account:

• Backed directly by the U.S. government. Not FDIC insurance — actual U.S. Treasury obligations. The strongest guarantee in financial markets.

• Interest is exempt from state and local income tax. Federal tax only. This is the line that changes the math.

• You can auto-roll them. Set up your brokerage or TreasuryDirect to automatically reinvest into a new 4-week bill every time one matures. Cash on a 28-day treadmill, indefinitely.

Why state-tax exemption matters more than people realize

This is the piece nearly every article on T-bills glosses over. Let’s run the after-tax math at the same income level.

Assume you’re in a 24% federal bracket and pay 9% combined state and local (close to NYC, NJ, CA, MD). Your savings account interest gets hit by BOTH layers. Your T-bill interest only gets hit by federal.

Top high-yield savings on the market: 4.10% gross. After 24% federal + 9% state = 2.75% after tax.

Average high-yield savings: 1.58% gross. After tax: 1.06%.

4-week T-bill: 3.61% gross. After 24% federal only (no state) = 2.74% after tax.

The 4-week T-bill effectively ties the top HYSA on after-tax yield, while crushing the national average. And it does it with zero promotional-rate games and the strongest credit backing on earth.

How to actually buy one

Two paths.

Path 1: Through your existing brokerage. Fidelity, Schwab, and Vanguard all let you buy T-bills directly. Auto-roll is built into the platform. Free to trade — no commissions on Treasury purchases. This is what most people should do. It lives next to your other accounts. The cash sweep + auto-roll feels exactly like a savings account.

Path 2: Through TreasuryDirect.gov. Same product, different interface. The advantage is direct relationship with the Treasury and no possibility of broker errors. The disadvantage is the website is from 1998 and recovering a locked account is a nightmare. For most people, doing it through Fidelity or Schwab is simpler.

Action this week: Open the bond/fixed-income screen at Fidelity, Schwab, or Vanguard. Look for ‘Treasury auction’ or ‘New issue treasuries.’ Buy a 4-week T-bill in any amount you’d otherwise keep in a savings account. Check the box for auto-roll. That cash is now earning state-tax-exempt yield, government-backed, with no bank promotional rate to babysit. Takes 10 minutes once you find the screen.

When HYSA still wins

Two scenarios where I’d keep money in a high-yield savings account.

If you might need the cash mid-month. T-bills mature in 4-week blocks. If you have to liquidate before maturity, you sell on the secondary market — usually painless, but you’re at the mercy of where rates have moved that week. A HYSA gives you instant access, full stop.

If you live in a no-income-tax state. Texas, Florida, Tennessee, Washington, etc. The state-tax exemption doesn’t help you, and HYSA top rates (4.10% gross) edge out the 4-week T-bill (3.61%). In those states, the math swings back to favor a top HYSA.

The one-line version

Cash management hasn’t gotten easier in 2026. It’s gotten more rewarding for people who know the rules. T-bills aren’t exotic. They’re not risky. They’re the Treasury paying you not to leave your money at a bank — and in any state with income tax, that’s a deal worth taking.

Sources

• Federal Reserve H.15 — Daily Treasury rates (June 2026) — https://www.federalreserve.gov/releases/h15/

• Experian — Average savings account interest rates (June 2026) — https://www.experian.com/blogs/ask-experian/average-savings-account-rates/

• Bankrate — Best high-yield savings accounts (June 2026) — https://www.bankrate.com/banking/savings/best-high-yield-interests-savings-accounts/

• Public.com — How Treasury bills are taxed — https://public.com/learn/how-are-treasury-bills-taxed

• TreasuryDirect — Buying T-bills — https://www.treasurydirect.gov/marketable-securities/treasury-bills/

Disclaimer

Affluent Notes is for educational and entertainment purposes only. Nothing in this newsletter is financial, tax, legal, or investment advice. The numbers, charts, and strategies discussed are illustrative; your situation, tax bracket, plan rules, and risk tolerance are different. Past performance does not guarantee future results. Talk to a licensed CPA, CFP, or attorney before acting on anything you read here. The author may hold positions in securities or accounts mentioned.