What Is an HSA?

A health savings account is a tax-advantaged account you own personally and use to pay for qualified medical expenses, things like deductibles, copays, prescriptions, dental, and vision. You can only open and contribute to one if you are enrolled in a high-deductible health plan, or HDHP, and are not on Medicare or claimed as someone else's dependent. The pairing is the whole point: a high-deductible plan keeps your premiums lower but exposes you to more out-of-pocket cost, and the HSA is the tax-favored bucket meant to cover that cost.

Two features set the HSA apart from most health accounts. First, the money is yours: it rolls over in full every year, never expires, and stays with you when you change jobs or insurers. Second, it can be invested. Above a small cash minimum, many providers let you put the balance into funds where it can grow over time. That combination, permanent ownership plus investability, is why the HSA is discussed as a long-term account rather than a use-it-or-lose-it spending account.

The HSA's reputation rests on one feature: it is untaxed at all three stages of an account's life. Money going in is tax-deductible, so a contribution lowers your taxable income for the year (and if you contribute through payroll, it comes out pre-tax). Money inside grows tax-free, meaning the interest, dividends, and investment gains are not taxed year to year the way a regular brokerage account is. And money coming out for qualified medical expenses is tax-free, with no tax owed on the withdrawal at all.

Compare that to the accounts most people know. A traditional 401(k) gives you the deduction going in but taxes withdrawals. A Roth IRA taxes contributions but frees the withdrawals. A taxable brokerage account taxes the growth along the way. The HSA is the only common account that skips tax at every stage for medical spending, which is exactly why it is so prized by people who plan around it.

The IRS resets the numbers each year. For the 2026 tax year, the HSA contribution limit is $4,400 for self-only coverage and $8,750 for family coverage. If you are 55 or older you can add a $1,000 catch-up contribution on top, and if both spouses are 55 or older each can make a catch-up in their own account. These limits cover the total from all sources, including anything your employer puts in.

To contribute, your health plan has to qualify as a high-deductible plan. For 2026 that means a deductible of at least $1,700 for self-only coverage or $3,400 for family coverage, with total out-of-pocket maximums no higher than $8,500 (self-only) or $17,000 (family). Premiums do not count toward that out-of-pocket cap. These are the 2026 figures and they change annually; confirm the current limits and your plan's eligibility with the IRS before you contribute. Our HSA contribution limits guide breaks down the numbers and the year-over-year changes.

Here is the part most people miss. Because the balance rolls over forever and can be invested, an HSA can work as a long-term, tax-free investment account, not just a fund for this year's copays. The strategy some people use: contribute the maximum, pay current medical bills out of pocket with other money, and leave the HSA invested to grow for years or decades. Inside the account the money can sit in broad index funds, for example a total-market or S&P 500 fund like VOO or VTI, depending on what your provider offers.

The mechanism that makes this work is that the IRS does not require you to reimburse a medical expense in the year it happens. As long as the expense occurred after you opened the HSA, you can save the receipt and reimburse yourself tax-free at any point in the future. So a bill you paid out of pocket today can become a tax-free withdrawal years from now, after the balance has grown. That is why the HSA gets called a stealth or backdoor retirement account: it can deliver tax-free growth like a Roth while also having given you a deduction up front. Whether this approach fits depends on whether you can afford to pay current medical costs without touching the account, and on your own finances. Walnut is not a financial or tax advisor, so treat this as a description of how the account works, not a recommendation.

At 65 the rules loosen. Before then, taking money out for anything other than a qualified medical expense costs you ordinary income tax plus a 20% penalty. Once you turn 65 that 20% penalty disappears, so a non-medical withdrawal is taxed simply as ordinary income, which makes the HSA behave just like a traditional IRA for general spending. Withdrawals for qualified medical costs remain tax-free at any age, and after 65 that includes many Medicare premiums (Part B, Part D, and Part C).

One catch worth flagging: enrolling in Medicare ends your ability to contribute. Starting the month your Medicare coverage begins, your HSA contribution limit drops to zero, even though you can keep spending the balance you already built. This Medicare interaction trips people up, so plan timing carefully and verify the specifics with the IRS or a tax professional.

HSAs are often confused with FSAs (flexible spending accounts), but they behave very differently. The biggest gap is ownership and rollover. An HSA is yours permanently, rolls over in full every year, and can be invested. An FSA is owned by your employer, is largely use-it-or-lose-it, and cannot be invested. For 2026 the health FSA contribution limit is around $3,400, with an optional carryover (up to roughly $680 if your employer allows it) rather than the unlimited rollover an HSA gives you.

The other key difference is the plan requirement. An HSA requires a high-deductible health plan; an FSA does not, so you can have an FSA with almost any employer plan. The trade-off is that the FSA's deadline pressure and lack of portability make it a spending tool for the year, while the HSA's permanence and investability are what let it double as a long-term account. Our FSA vs HSA guide compares the two side by side.

The table is the whole pitch in three rows: untaxed in, untaxed while it grows, untaxed out for medical costs. Figures and rules in this guide reflect the 2026 tax year and can change; verify the current numbers and the definition of a qualified medical expense with the IRS before acting.

An HSA is a personal medical-spending account that pairs with a high-deductible health plan and carries a triple tax advantage no other common account matches: deductible contributions, tax-free growth, and tax-free withdrawals for qualified medical costs. For 2026 you can contribute up to $4,400 self-only or $8,750 family, plus a $1,000 catch-up at 55 or older, as long as your plan meets the HDHP requirements. The balance is yours for life and rolls over every year.

Used as a simple spending account it covers your medical costs with pre-tax dollars. Used deliberately, invested and left to grow while you pay current bills out of pocket, it can act as a stealth retirement account with tax-free growth, and after 65 it behaves much like a traditional IRA for any spending. The right approach depends entirely on your own finances and tax situation. Walnut is informational and is not a financial or tax advisor; this is not tax advice, so verify every figure with the IRS and consider a qualified professional.