High-Yield Savings vs Treasury Bills: Maximizing Liquid Cash Reserves
An emergency fund or a down-payment reserve has one job: be there, in full, when you need it. Within that constraint, the two most popular homes for idle cash are a high-yield savings account (HYSA) and short-term U.S. Treasury bills. They often advertise similar headline rates, but they differ in how they are taxed, how fast you can reach the money, and what protects your principal. Those differences decide which one actually pays you more.
This guide walks through the mechanics, gives you a formula to compare the two on an after-tax basis, and shows a simple structure that captures most of the benefit of each.
- T-bill interest is exempt from state and local income tax; HYSA interest is not.
- If you live in a state with no income tax, compare the two rates almost directly.
- In a high-tax state, a T-bill can beat a HYSA paying a noticeably higher headline rate.
- A HYSA wins on instant access; T-bills win on government backing with no $250,000 cap.
- Most people do best with a split: one month of expenses in a HYSA, the rest in a short T-bill ladder.
How Each Option Actually Works
A high-yield savings account is a bank deposit. The bank pays a variable rate, usually quoted as an APY that already includes compounding, and it can change that rate at any time. Deposits are protected by FDIC insurance (or NCUA insurance at credit unions) up to $250,000 per depositor, per insured institution, per ownership category.
A Treasury bill is a short-term loan to the U.S. government. Bills are sold at a discount to face value and pay the full face value at maturity; the difference is your interest. The Treasury currently auctions bills with maturities of 4, 6, 8, 13, 17, 26 and 52 weeks, in increments of $100. You can buy them at auction through TreasuryDirect.gov or through most brokerages, and both let you set up automatic reinvestment when a bill matures. Because your rate is locked at auction, a T-bill protects you from a falling rate for its term, while a HYSA rate can be cut the next day.
| Feature | High-Yield Savings | Treasury Bills |
|---|---|---|
| Rate type | Variable, can change any day | Fixed until maturity |
| Federal income tax | Yes | Yes |
| State and local income tax | Yes | Exempt |
| Principal protection | FDIC/NCUA up to $250,000 per category | Full faith and credit of the U.S., no cap |
| Access to cash | Transfer out, usually 1β2 business days | At maturity, or sell early at a brokerage |
| Minimum | Often $0 | $100 |
The After-Tax Math: When a Lower Rate Pays More
Headline rates are misleading because the two are taxed differently. HYSA interest is taxed at your federal rate plus your state (and sometimes city) rate. T-bill interest is taxed only at the federal level. To compare them fairly, find the HYSA rate you would need to match a given T-bill rate after tax.
Take an illustrative example, not a current market quote. Suppose a 13-week bill yields 4.00%, you are in the 24% federal bracket, and your state taxes interest at 9.3%. The T-bill keeps 4.00% Γ 0.76 = 3.04% after tax. A HYSA has to clear 3.04% Γ· (1 β 0.24 β 0.093) = 3.04% Γ· 0.667 β 4.56% just to tie. A savings account advertising 4.40% would look better on paper and still pay you less.
Now repeat the exercise for someone in Texas, Florida, Washington or another state without a personal income tax. The state term is zero, the formula collapses, and the break-even HYSA rate is simply the T-bill rate. In those states, you can compare the two numbers almost directly and choose on access and convenience.
One more detail: T-bill auction results quote an "investment rate", which is a simple-interest, bond-equivalent figure, while HYSAs quote APY with compounding. For short bills that are rolled over, the difference is small, but if two options are within a few hundredths of a percent, the compounding HYSA may edge ahead.
Liquidity: How Fast Can You Get Your Money Out?
For an emergency fund, access matters more than the last 0.2%. A HYSA is the simplest: you transfer money to checking and it usually arrives within one or two business days. The Federal Reserve removed the old six-withdrawals-per-month rule for savings accounts in 2020, but some banks still enforce their own limits, so check your account terms.
T-bills are designed to be held to maturity. Where you hold them changes how flexible they are:
- At a brokerage: you can sell a bill before maturity on the secondary market. The price moves with interest rates, so you might get slightly more or less than you paid plus accrued interest. Treasury trades generally settle the next business day.
- At TreasuryDirect: you cannot sell before maturity on the site. To sell early you must first transfer the bill to a brokerage, and TreasuryDirect requires you to hold a security for 45 days before it can be transferred.
- Either way: if you choose maturities that line up with when you might need cash, you rarely need to sell early at all.
Safety: FDIC Limits vs Government Backing
Both options are about as safe as cash gets, but the protections work differently. FDIC insurance covers up to $250,000 per depositor, per insured bank, per ownership category. If your reserve is larger than that, for example after selling a house, you need to spread it across banks or ownership categories to stay fully covered. Also confirm that a fintech "savings" product is actually held at an FDIC-insured partner bank, and in an account titled in a way that passes insurance through to you.
Treasury bills are direct obligations of the U.S. government, with no dollar cap. For very large cash balances, that is the main reason businesses and high-net-worth households favor T-bills or government money market funds.
Video Walkthrough: Buying Your First T-Bill
If you have never bought a Treasury bill, this walkthrough by Charlie Chang shows the account setup and purchase screens step by step. It was recorded in 2023, so the yields mentioned in it are not today's rates; focus on the process.
A Practical Structure: The Two-Tier Cash Reserve
You do not have to choose one. A simple setup gets most of the tax advantage of T-bills while keeping instant access for real emergencies:
- Tier 1, instant cash: keep roughly one month of essential expenses in a HYSA linked to your checking account.
- Tier 2, the ladder: split the rest of your reserve into equal parts in 4-, 8- and 13-week bills, staggered so that something matures every few weeks.
- Automate it: turn on auto-reinvestment so each maturing bill rolls into a new one unless you need the cash.
- Review twice a year: rerun the break-even formula with current rates and your current tax bracket, and shift the balance between tiers if the math changes.
A government money market fund at a brokerage is a reasonable middle ground if you want T-bill-like yields with same-day or next-day access. Part of its income may be exempt from state tax, depending on how much of the fund is in U.S. government obligations and on your state's rules, so check the fund's annual tax information before counting on it.
This article explains general mechanics. Tax rules vary by state and by personal situation; confirm your own brackets and account terms, or ask a qualified tax professional, before moving large balances.
The bottom line: if you pay state income tax, run the break-even formula before chasing the highest advertised savings rate. If you do not, pick whichever option gives you the access you need, and keep at least a month of expenses one transfer away.