Where to park your cash

Idle cash is a quiet leak

Most people keep too much money in an account paying almost nothing while inflation chips away at it. The fix isn’t complicated — it’s knowing which home fits which money. There are three serious places to keep safe cash in the US: a high-yield savings account, I-Bonds, and Treasury bills. Each is government- backed or FDIC-insured, so the question isn’t whether your money is safe — it’s how much you earn and how fast you can get it back. This tool compares all three (plus a plain checking account) over the timeline you choose, and the guide below explains when to reach for each.

The three places to park cash

A high-yield savings account (HYSA) is the workhorse. It’s an online savings account that pays many times what a big bank pays on its standard savings, and it’s the most liquid of the three — you can move money in and out any day, and deposits are FDIC-insured up to $250,000 per bank. The rate is variable, so it floats up and down as the Federal Reserve moves. That makes it the natural home for an emergency fund and any cash you might need on short notice. It suits almost everyone, which is why it’s the default answer for most savers.

I-Bonds are savings bonds issued by the US Treasury and bought directly at TreasuryDirect.gov. Their rate has two parts — a fixed rate set for the life of the bond and an inflation rate that resets every six months based on the CPI. When inflation runs hot, I-Bonds shine; when it cools, the headline rate falls with it. The catch is access: you cannot redeem an I-Bond at all for the first 12 months, and you’re capped at $10,000 per person per year. They suit money you’re confident you can leave alone for a few years and want shielded from inflation.

Treasury bills (T-bills) are short-term US government debt sold at a discount and maturing in a few weeks up to 52 weeks. You buy at, say, $980 and receive the full $1,000 at maturity — the difference is your yield, locked in the day you buy. They’re sold at TreasuryDirect or through any brokerage. T-bills suit a known timeline (a tax bill due in six months, a down payment you’ve dated) and high earners in income-tax states, because the interest is exempt from state and local tax.

How to use this tool

It takes two inputs. First, type the amount of cash you’re deciding about — the real number sitting in checking or a low-rate savings account, whether that’s $2,000 or $50,000. Second, pick your time horizon: how long this money can realistically stay put, from three months to five years. The tool then races each option side by side, showing what you’d earn and your ending balance, and flags the winner for that timeline. Try a few horizons — you’ll see the ranking shift as the window lengthens, which is exactly the trade-off you’re weighing.

A worked example: $10,000 for 12 months

Say you have $10,000 you won’t touch for a year. At the rates loaded in the tool (which move over time — always check today’s numbers), a high-yield savings account earning around 4.9% returns roughly $490. A 1-year T-bill near 4.2% returns about $420 and is state-tax-free. An I-Bond around 4.26% earns close to $426 but can’t be touched for the full 12 months. Leaving the same $10,000 in a typical checking account at 0.4% earns about $40. The spread between the best option and checking is roughly $450 — for the same money, the same year, the same zero risk. That gap is the entire point: cash that does nothing is leaving real money on the table. Note that when inflation spikes, the I-Bond can leap ahead of savings; when it cools, savings or a T-bill often wins. Rerun the tool with current rates before you decide.

Taxes and rules that matter

• HYSA: interest is fully taxable as ordinary income at both the federal and state level. In exchange you get instant access and FDIC insurance up to $250,000 per bank, per depositor.
• I-Bonds: interest is exempt from state and local tax, and federal tax is deferred until you redeem (or the bond hits 30 years). Remember the 12-month lockup, and if you cash out before five years you forfeit the last three months’ interest — so plan to hold at least five years to keep every dollar.
• T-bills: interest is exempt from state and local tax but taxable federally, which is what makes them attractive to high earners in high-tax states. You commit until maturity, though you can sell early on the secondary market through a broker if you must.

Common mistakes

• Locking up money you’ll actually need. An I-Bond’s 12-month lockup or a T-bill’s maturity date is a problem if your car dies next month. Match the lockup to a timeline you’re sure of.
• Chasing yield over access. A tenth of a percent more isn’t worth being unable to reach your emergency fund. For money you might need any day, liquidity wins every time.
• Leaving cash in a 0.01% big-bank account. This is the most common and most expensive mistake. The big national banks pay almost nothing on savings; moving to a high-yield account is a five-minute fix that can pay for itself many times over.

Related tools and guides

You won’t get rich on cash, and that’s fine — its job is to stay safe and keep up with prices. Pairing the right account with the right timeline turns a guaranteed loss to inflation into a small, dependable gain. See how much inflation is eroding your money, and check whether your pay is keeping up with the raise vs inflation tool. For a step-by-step on putting idle savings to work, read what to do if you have $1,000 or more in the bank, and to automate the whole thing see our roundup of the best personal finance apps. Browse every calculator to plan the rest of your money. This is general information, not financial advice.