If you hold emergency savings or short-term cash in a High-Yield Savings Account (HYSA) paying 4.50% to 5.00% APY, you might think you are maximizing your risk-free returns. But for professionals living in high-income-tax states like California, New York, New Jersey, Massachusetts, or Virginia, there is a hidden drag on your earnings: state and local income taxes.
Every dollar of interest earned in an HYSA or standard bank Certificate of Deposit (CD) is fully taxed as ordinary income at both the Federal and State levels. However, under federal statute (31 U.S.C. § 3124), interest on U.S. Treasury Bills (T-Bills) is 100% exempt from all state and local income taxes.
Below is the mathematical breakdown of the Tax-Equivalent Yield (TEY) across different state tax brackets, why you should avoid TreasuryDirect in favor of brokerage auto-roll systems (Fidelity/Schwab), and how to verify the exemption on your year-end Form 1099-INT Box 3.
📌 T-Bills vs. HYSA: Fundamental Comparison
- Backing: Full faith and credit of the U.S. Government (T-Bills) vs. FDIC insurance up to $250k/institution (HYSA).
- Federal Income Tax: Both are subject to Federal income tax (ordinary rates).
- State & Local Income Tax: 0% on T-Bills (100% Exempt) vs. Fully Taxed on HYSA.
- Maturity Terms: 4-week, 8-week, 13-week, 17-week, 26-week, and 52-week terms.
1. The Tax-Equivalent Yield (TEY) Mathematical Formula
Because T-Bills bypass state income taxes entirely, a lower nominal T-Bill rate often yields more take-home cash than a higher headline HYSA rate. To compare them objectively, we calculate the Tax-Equivalent Yield (TEY):
🧮 The Tax-Equivalent Yield Formula:
Tax-Equivalent HYSA Yield = Nominal T-Bill Rate ÷ (1 — Marginal State Tax Rate)
State-by-State Real-World Yield Comparison (Assuming a 4.60% 4-Week T-Bill)
Let’s look at how much a 4.60% T-Bill is actually worth compared to an HYSA across various state tax brackets:
| State / Location | Marginal State Tax | Nominal T-Bill Rate | Required HYSA APY to Match |
|---|---|---|---|
| California (Middle Bracket) | 9.30% | 4.60% | 5.07% APY |
| California (Top Bracket) | 13.30% | 4.60% | 5.31% APY |
| New York City (NY State + NYC) | 10.75% | 4.60% | 5.15% APY |
| New Jersey | 6.37% – 8.97% | 4.60% | 4.91% – 5.05% APY |
| Massachusetts (Flat Rate) | 5.00% | 4.60% | 4.84% APY |
| TX, FL, WA, NV (No State Income Tax) | 0.00% | 4.60% | 4.60% APY (Tie) |
The Takeaway: If you live in California or NYC, an HYSA advertising 4.75% actually pays you less after-tax cash than a 4.60% T-Bill. On a $100,000 cash balance, the state tax difference puts $350 to $700+ extra cash per year directly into your pocket.
2. Why You Should NOT Use TreasuryDirect (The Brokerage Advantage)
When people first learn about T-Bills, they often go to TreasuryDirect.gov. While functional, TreasuryDirect has severe real-world friction:
- Outdated UI & Access: Clunky virtual keyboard login, account lockouts, and notoriously slow customer service.
- Illiquidity: If you need emergency cash before maturity, TreasuryDirect does not support secondary market trading. You must transfer the security to a commercial brokerage, which can take weeks.
💡 The Better Route: Buy via Fidelity, Charles Schwab, or Vanguard
- $0 Commission: Major brokerages charge zero fees to participate in Treasury auctions or trade secondary T-Bills.
- Instant Liquidity: If you need your cash tomorrow, you can sell your T-Bill on the secondary market with one click during market hours.
- Automated Auto-Roll: When your 4-week or 13-week T-Bill matures, the principal automatically purchases the next newly auctioned T-Bill without you lifting a finger.
3. Step-by-Step: How to Set Up Auto-Rolling T-Bills on Fidelity / Schwab
- Navigate to Fixed Income: Log into your brokerage account and select News & Research > Fixed Income, Bonds & CDs.
- Select Treasury Auctions: Choose Treasuries > Auction (to buy newly issued bills at wholesale auction prices without a bid-ask spread).
- Choose Your Maturity:
- 4-Week (1-Month): Best for maximum liquidity.
- 13-Week (3-Month): Often slightly higher yield with a quarterly reset.
- Enter Quantity: T-Bills have a $1,000 face value (par). Enter the number of bonds (e.g., quantity 10 = $10,000 face value). Note that T-Bills are zero-coupon: you buy at a discount (e.g., $9,965) and receive the full $10,000 at maturity.
- Enable Auto-Roll: Check the box for Auto-Roll. Your brokerage will automatically reinvest the principal at each maturity cycle until you toggle it off.
4. Tax Season Confirmation: Form 1099-INT Box 3
When tax season arrives, your brokerage will issue a consolidated Form 1099-INT:
- Box 1 (Total Interest Income): Contains standard bank/HYSA interest (taxed by both IRS and your State).
- Box 3 (Interest on U.S. Savings Bonds and Treasury Obligations): Contains your T-Bill earnings.
When you import your 1099-INT into software like TurboTax, TaxAct, or FreeTaxUSA, the program automatically pulls Box 3 into your Federal return while subtracting it 100% from your State tax return. No manual exemption forms or complex schedules required.
5. Final Verdict: When to Pick T-Bills vs. HYSA
- Keep in HYSA: Your immediate monthly spending float (1 month of living expenses) where you need checking account ACH connectivity and instant same-day debit access.
- Move to Auto-Rolling T-Bills: Your true emergency fund (3–6 months of living expenses) or large short-term cash reserves (home down payment, annual property tax fund, tuition fund), especially if you live in CA, NY, NJ, MA, or any state with an income tax rate above 4%.
Disclosure: This article is for informational and educational purposes based on current federal statutes and state tax codes. DCLifeLab is not a licensed CPA or investment advisor. Verify your state marginal tax rate before executing tax arbitrage strategies.