Where Should You Keep Your Cash: HYSA, T-Bills, or Money Market?

Once a cash balance gets past a few thousand dollars, "just put it in savings" stops being a complete answer. The natural follow-up is where, exactly. A high-yield savings account, a Treasury bill, a money market fund, and a money market deposit account can all hold cash, and threads asking "T-bill vs HYSA" or "what's the difference between a money market fund and a money market account" turn up constantly once a balance is large enough that the choice actually changes the outcome. Below a certain size, the differences barely register. Above it, insurance, liquidity, and taxes all start to matter enough to work out on purpose.

This post covers how each vehicle works, which one fits which kind of cash, and the tax wrinkle that gives Treasury bills a real edge over savings accounts once you're in a state with income tax. If the open question for you is how much cash to hold in the first place rather than where to put it, how much cash is too much covers that separately.

The four places cash actually lives

A high-yield savings account is a savings account, usually at an online bank or a fintech partnered with one, that pays a materially higher rate than a traditional brick-and-mortar savings account. It's FDIC-insured up to the standard limit, the balance is available immediately inside the bank's own ecosystem, and an ACH transfer out typically lands in one to three business days. The rate floats with prevailing short-term rates, so it can drop without warning.

A money market deposit account (MMDA) is a close cousin, also offered by banks, also FDIC-insured, also variable-rate. The practical difference from a HYSA is mostly institutional: some banks pair an MMDA with check-writing or debit access that a plain savings account doesn't offer, and the two products sometimes carry different minimum balance requirements at the same bank. For the purpose of deciding where to park cash, treat an MMDA the same way you'd treat a HYSA.

A money market fund (MMF) is a mutual fund, not a bank account. It pools investor money into very short-term, high-quality debt: Treasury bills, short-term corporate paper, repurchase agreements. Money invested in a money market fund is not FDIC-insured, because it's a security, not a deposit, a distinction the SEC's investor education office spells out explicitly for exactly this reason. Funds are managed to keep a stable share price and have an excellent track record, but a track record is not the same guarantee as federal deposit insurance. Redemptions typically settle within one business day.

A Treasury bill is a short-term debt obligation of the U.S. government, sold at a discount and maturing at face value, with terms currently running from four weeks to a year. It isn't FDIC-insured because it isn't a bank product at all; it's backed directly by the federal government instead. You can buy T-bills through TreasuryDirect.gov or through a brokerage account, hold them to maturity, or sell them on the secondary market before maturity if your plans change.

The mix-up that actually costs people money

The most common confusion in this space, and the reason the question keeps resurfacing on forums, is treating "money market fund" and "money market account" as the same thing. They aren't. A money market deposit account is a bank product with FDIC insurance behind it. A money market fund is an investment product with no FDIC insurance behind it. The names are close enough that banks and brokerages both use "money market" in their marketing, and the distinction gets lost in the process.

In practice this rarely causes a loss, because money market funds hold extremely short-term, high-quality debt and have a long history of maintaining a stable share price. But a strong history and federal insurance are different claims, and if deposit insurance is specifically the feature you're paying for peace of mind, know which of the two products you actually hold. Check your statement: if it says "deposit account," you're FDIC-insured. If it shows a fund name or a ticker, you're not.

How fast you can actually get the money

A HYSA is the fastest of the three. The balance is available immediately for transfers within the same bank, and a standard ACH transfer to an outside account typically lands in one to three business days.

A money market fund settles close behind. A redemption placed on a business day typically pays out the next business day to a linked bank account.

A T-bill depends on whether you hold it to maturity or sell early. Held to maturity, the face value pays out on the maturity date, no earlier and no later, so a T-bill only fits money you don't need before a specific date. Sold early on the secondary market, T-bills are highly liquid, especially recently auctioned ones, and a broker can typically execute the sale the same day. But the price you get depends on where interest rates have moved since you bought it: rates up, price down, and you can receive less than face value if you need to exit during a period of rising rates. That price risk is the tradeoff for the tax and yield advantages below, and it's why T-bills work best for money with a known date rather than money you might need on any given Tuesday.

The tax angle, and why it grows with the balance

This is where Treasury bills pull ahead of savings accounts for a specific group of people, and it's easy to miss because it doesn't show up until you compare after-tax numbers side by side.

Interest from a HYSA or an MMDA is fully taxable: federal income tax, plus state and often local income tax if your state levies one. Interest from a T-bill is taxable at the federal level but exempt from state and local income tax, under the federal statute that exempts direct obligations of the U.S. Treasury from state and local taxation. Some money market funds that hold mostly Treasury securities pass through part of that exemption too, though the treatment varies by fund and by state, so check the fund's own tax documentation rather than assuming.

If your state has no income tax, this doesn't move the needle. If you're in a high-tax state, it can be a real chunk of the return.

A worked example, using an assumed yield for illustration only: assume a HYSA and a T-bill both currently yield around 4.5%, a plausible rate as of this writing that will not stay accurate for long and should not be treated as a forecast. Assume $100,000 in cash, a 32% federal marginal tax rate, and a 9% state income tax rate, roughly the upper-bracket rate in a high-tax state like California or New York.

At 4.5%, $100,000 earns $4,500 in interest over the year in either vehicle.

• HYSA: $4,500 in interest, taxed at 32% federal plus 9% state, for $1,845 in combined tax. After-tax return: $2,655, an effective after-tax yield of 2.655%.
• T-bill: $4,500 in interest, taxed at 32% federal only. Tax owed: $1,440. After-tax return: $3,060, an effective after-tax yield of 3.06%.

The gap is $405 a year on $100,000, coming entirely from the state tax exemption, with the gross yield held identical between the two vehicles. Scale that to $250,000 and it's roughly $1,013 a year. The gap grows with your state tax rate and shrinks toward nothing in states with no income tax, so run your own bracket before assuming this applies to you.

Matching the vehicle to the money

The right answer depends on what job the cash is doing, not on which vehicle has the best marketing.

Emergency fund. This money needs to be available on short notice, in full, without price risk. A HYSA or MMDA is the right home: FDIC-insured, immediately available, no chance of showing up worth less than you put in because rates moved. The tax drag on a HYSA is real but small next to the value of not having to sell something at a bad time to cover a genuine emergency.

Money with a known date, roughly one to twelve months out. A house down payment closing in four months, a tax bill due in March, a wedding deposit next spring. T-bills fit well here: match the maturity to the date you need the cash, hold to maturity to avoid price risk entirely, and pick up the state tax exemption along the way. A money market fund also works if you want flexibility without committing to a specific maturity date.

A large cash cushion beyond your emergency fund, the kind covered in how much cash is too much, where the honest answer for most of it is usually to invest it rather than park it. For the portion you've deliberately decided to keep in cash, T-bills or a Treasury money market fund are typically the more tax-efficient home once the balance is large enough that the state tax difference stops being a rounding error.

If the open question for you is how to prioritize cash against retirement accounts and debt paydown in the first place, savings order of operations is the place to start; this post assumes you already know how much cash you want to hold and is only about where it sits once that decision is made.

None of this calls for splitting your cash across four account types to optimize every dollar. For most people, one HYSA for the emergency fund and, once the balance justifies the effort, a T-bill ladder or a Treasury money market fund for dated money and the excess cushion, covers the whole picture. If you track your full financial position in Steady Wealth, cash across every account rolls up into one allocation number regardless of which specific vehicle each dollar sits in, so none of this complicates the tracking side of things.

Frequently asked questions

Are money market funds FDIC insured?

No. A money market fund is a mutual fund, and mutual funds are securities, not bank deposits, so FDIC insurance doesn't apply. A money market deposit account, a similarly named but different product offered directly by a bank, is FDIC-insured up to the standard limit. Check your statement to see which one you actually hold.

Is a HYSA or a T-bill better?

Neither is universally better; they fit different jobs. A HYSA suits money you might need on short notice, since it carries no price risk and settles in one to three days. A T-bill suits money with a known date you can match to a maturity, and it carries a tax advantage in states with income tax, since T-bill interest is exempt from state and local tax.

How much cash should I keep liquid versus in Treasury bills?

Keep your full emergency fund liquid in a HYSA or MMDA, since you can't predict when you'll need it. Money with a specific date attached, from a few weeks out to a year, is a good candidate for a T-bill matched to that date. How much cash is too much walks through sizing the emergency fund itself.

What's the current FDIC insurance limit?

$250,000 per depositor, per FDIC-insured bank, per ownership category, according to the FDIC. A joint account, an individual account, and a retirement account at the same bank are each insured separately, so a household can hold well over $250,000 at a single bank and still be fully covered if the accounts are structured across ownership categories.

Do I have to buy Treasury bills directly from the government?

No. You can buy them through TreasuryDirect.gov, in $100 increments, or through a brokerage account, where they trade in similar increments and can be sold on the secondary market before maturity if your plans change. Buying through a brokerage is usually more convenient if you already hold other investments there, since the T-bill shows up alongside everything else instead of in a separate government portal.

Does it make sense to ladder T-bills instead of buying one at a time?

For money with rolling near-term needs, yes. A ladder with staggered maturities, four-week, thirteen-week, twenty-six-week, and fifty-two-week bills for example, means a portion matures on a regular schedule, giving periodic access to cash without guessing a single date and without having to sell early if your timeline shifts.