Where to park cash: HYSA vs. money market vs. CD vs. T-bills

Once you have cash worth optimizing — an emergency fund, a down payment, a tax bill due in April — you'll notice there isn't one 'safe place for cash.' There are at least four, and they differ on the three things that matter: yield, access, and taxes. None of them is wrong. But each one is best for a specific job, and putting the right money in the wrong vehicle costs you either interest or liquidity.

The stakes are bigger than they sound. On $30,000 of savings, the gap between a megabank checking account at 0.01% and a competitive cash vehicle at roughly 4% is about $1,200 a year — every year, for doing nothing differently except picking a better parking spot. And the gap between the four good options, chosen well or badly for your situation, can still run a few hundred dollars a year in yield or a painful penalty at exactly the wrong moment. Ten minutes of matching money to vehicle is some of the best-paid work in personal finance.

The four contenders at a glance

• High-yield savings account (HYSA): variable rate, FDIC-insured, money out in 1–2 business days. The default.
• Money market fund (at a brokerage): variable rate that tracks the Fed almost instantly, not FDIC-insured but holds government debt, money out in 1 business day.
• Certificate of deposit (CD): fixed rate locked for a set term, FDIC-insured, early exit costs a penalty (typically 3–12 months of interest).
• Treasury bills (T-bills): fixed rate for 4–52 weeks, backed directly by the US government, interest exempt from state and local income tax.

HYSA: the flexible default

A good online HYSA pays a competitive variable rate with zero commitment. The catch is the word 'variable' — the bank can cut your rate any day, and banks are quicker to cut than to raise. HYSAs also play marketing games: teaser rates for new customers, or a flagship rate on a new product while your older account quietly lags. It's the right home for money you might need on short notice and for anyone who values simplicity over the last 0.2%.

What the rate games look like in practice: you open an account paying 4.4%, and eighteen months later it's paying 3.6% while the same bank advertises 4.3% on a nearly identical product with a different name. On $25,000, that quiet 0.7% drift is $175 a year for not noticing. The fix is a two-minute rate check twice a year — you don't need to chase every leader, just make sure your bank hasn't demoted you to the legacy-customer tier.

Money market funds: the rate-tracker

A money market fund (like Vanguard's VMFXX or Fidelity's SPAXX) is a mutual fund that holds ultra-short government and bank debt. Its yield follows the Fed's rate within days — no games, no loyalty penalty. It's not FDIC-insured, but government money market funds are considered extremely safe, and many brokerages sweep your idle cash into one automatically. If your cash already lives at a brokerage, this is usually the path of least resistance.

One detail worth knowing: because a chunk of these funds' holdings is Treasury debt, a portion of the interest is usually exempt from state income tax — the fund publishes the percentage each January. In a high-tax state, a Treasury-only money market fund (like VUSXX) pushes that exemption near 100%, quietly turning a 4.2% yield into something closer to a 4.5% taxable-equivalent yield for a Californian in the 9.3% bracket. Same account, same click, better after-tax math.

CDs: paying you to commit

A CD trades flexibility for certainty: you lock a fixed rate for 6 months to 5 years. That's a losing trade when rates are rising, and a winning one when rates are about to fall — a 12-month CD at 4.5% keeps paying 4.5% even if the Fed cuts three times. CDs shine for money with a known date: a tuition bill next August, a car purchase in 18 months. Just size the term so it matures before you need the cash, because the early-withdrawal penalty eats months of interest.

Run the penalty math before you commit, not after. Put $20,000 in a 12-month CD at 4.0% and break it at month five with a 6-month interest penalty: you've earned about $333 and forfeit about $400 — you walk away with less interest than a plain savings account would have paid, and in some fine print the penalty can even nick principal. The lesson isn't that CDs are bad; it's that a CD is only for money whose spend date you actually believe.

T-bills: the state-tax cheat code

Treasury bills are short-term IOUs from the US government, bought through any brokerage or TreasuryDirect. They pay rates similar to the best CDs, but the interest is exempt from state and local income tax — a real edge in high-tax states. Unlike a CD, there's no early-withdrawal penalty; if you need out, you sell the bill on the open market, usually at a tiny gain or loss depending on rates.

Ladders: the middle ground between locked and liquid

If you like fixed rates but hate the all-or-nothing lockup, ladder it. Split the money across several CDs or T-bills with staggered maturities so something is always coming due soon. You get most of the yield certainty of locking up, plus a scheduled exit every few weeks or months — and if rates rise, each maturing rung gets reinvested at the new, higher rate.

1. 1
   Split the pile

   Take the money you won't need immediately — say $12,000 — and divide it into four equal rungs of $3,000.

2. 2
   Stagger the maturities

   Buy 3-, 6-, 9-, and 12-month T-bills (or CDs). Now one rung matures every quarter, forever, if you keep rolling.

3. 3
   Roll or spend at each maturity

   When a rung matures, either spend it (if the goal arrived) or reinvest it at the longest term in your ladder at whatever rates are then.

4. 4
   Automate it

   TreasuryDirect and most brokerages offer auto-reinvestment on T-bills, so the ladder runs itself after setup.

How to choose in 30 seconds

1. Money you might need any time (emergency fund): HYSA or a government money market fund.
2. Money with a known spend date (tuition, car, wedding): a CD or T-bill maturing just before the date.
3. Money sitting at a brokerage between investments: the money market sweep fund is fine.
4. Live in a high-income-tax state? Tilt toward T-bills; the state-tax exemption is free yield.
5. Think rates are about to fall and won't need the cash soon? Lock a CD or a longer T-bill.

The bottom line

All four options are safe; the differences are access, rate behavior, and taxes. Keep instant-access money in an HYSA or money market fund, match CDs and T-bills to dates you actually know, and let your state tax rate break the ties. The worst choice isn't picking the wrong one of these four — it's leaving the cash in a megabank account earning 0.01% while you deliberate.