FSA vs. HSA: What Actually Separates Them

Both accounts let you pay for medical care with money that never got taxed. That is where the similarity ends. One of them belongs to you forever and can be invested; the other belongs to a plan year and can evaporate on December 31. Employers hand you both on the same enrollment screen with roughly the same font size, which is how people end up with the wrong one.

Who is even allowed to have each one

A health FSA comes from your employer. There's no income test and no coverage test — if your employer offers one, you can elect it. If you leave the job, you generally leave the account, and self-employed people can't have one at all.

An HSA has real eligibility rules, and they're checked month by month. Publication 969 lays them out: you must be covered by a qualifying high-deductible health plan on the first day of the month, you must have no other disqualifying health coverage, you must not be enrolled in Medicare, and you must not be claimed as a dependent on someone else's return. Miss any one of those and you aren't eligible for that month.

For 2026, a plan qualifies as a high-deductible health plan if the deductible is at least $1,700 for self-only coverage or $3,400 for family coverage, with out-of-pocket maximums no higher than $8,500 and $17,000. Note that both ends matter — a plan with a large deductible but an out-of-pocket maximum above the ceiling is not an HSA-qualified plan, regardless of what the brochure calls it.

The Medicare rule catches people who keep working past 65. Beginning with the first month you're enrolled in Medicare, your HSA contribution limit is zero. You can still spend what's already in the account; you just can't add to it.

The 2026 limits

• HSA: $4,400 for self-only coverage, $8,750 for family. Add $1,000 if you're 55 or older by the end of the year. Anything your employer puts in counts against your limit.
• Health FSA: $3,400 in salary reductions for plan years beginning in 2026. Employer contributions to a health FSA generally sit outside that cap, so check whether yours adds anything.
• Dependent care FSA: a separate account with a separate $7,500 exclusion for 2026 ($3,750 if married filing separately). It pays for childcare and adult daycare, not medical bills, and it plays by harsher rules than the health FSA — no carryover.

Use it or lose it, and the two escape hatches

The health FSA's defining feature is that unused money at the end of the plan year is forfeited. It goes back to the employer. You can't take cash instead, and you can't roll it into next year unless the plan says so.

There are exactly two ways a plan can soften that, and under IRS Notice 2013-71 a plan may adopt one of them, not both:

1. A grace period of up to two months and fifteen days after the plan year ends, during which you can keep incurring expenses against last year's money. For a calendar-year plan that runs to March 15.
2. A carryover of unused funds into the following plan year. The maximum carryover for 2026 plan years is $680, and an employer may set a lower limit than that. Carryover money does not count against next year's contribution limit.

Plenty of plans offer neither, in which case December 31 is a wall. Find out which arrangement yours has before you elect, not in the second week of December when you're buying reading glasses you don't need.

One genuine perk in the FSA's favor, and it's underrated: you must be able to receive the full amount you elected at any time during the coverage period, regardless of how much you've actually contributed so far. Elect $2,400, have $200 taken out in January, need $2,400 of dental work in February — the plan pays. And if you leave the job mid-year having spent more than you contributed, employers generally can't chase you for the difference.

The HSA does none of that, and doesn't need to

HSA money doesn't expire. Publication 969 puts it plainly: amounts left at the end of the year carry over, and the account is portable — "it stays with you if you change employers or leave the work force." Lose HSA eligibility and you simply stop contributing; the balance is still yours and can still be spent on qualified medical expenses forever.

It also invests. Most HSA custodians will move balances above some threshold into mutual funds, which turns the account into something closer to a retirement account with a medical label. Our separate guide on using an HSA as a long-term account goes further into that.

The rules that keep it honest: distributions not used for qualified medical expenses are taxable and carry an additional 20% tax, with no additional tax after you turn 65, become disabled, or die. And expenses incurred before you established the HSA are never qualified expenses — so open the account the day you become eligible, even if you fund it with $50, because the clock starts at establishment.

What the tax break is actually worth, with the arithmetic

Say you're in the 22% federal bracket, pay 7.65% in Social Security and Medicare tax, and live in a state with a 5% income tax. Your marginal rate on the next dollar of salary is roughly 34.65%.

Elect $3,000 into a health FSA and you avoid tax on $3,000: 0.3465 × $3,000 = $1,039.50 you keep.

Now forfeit $400 of it in December because you overestimated your dental year. Your net benefit is $1,039.50 − $400 = $639.50. Still positive — which is the point people miss when they refuse to elect anything for fear of forfeiting. At that marginal rate, you'd have to forfeit more than about a third of the election before it turned into a loss.

One detail on the HSA side that's worth real money: contributions made through your employer's payroll under a cafeteria plan escape Social Security and Medicare tax as well as income tax. If you instead write a check to your HSA custodian and deduct it on your return, you get the income tax break but not the 7.65%. On a $4,400 self-only contribution that difference is about $337. Route it through payroll if your employer lets you.

The limited-purpose FSA, which exists to solve one specific problem

You can't contribute to an HSA while you're covered by a general-purpose health FSA — including your spouse's, and including your own during a grace period with money still in it. That trips up more people than any other rule in this article.

The fix is a limited-purpose FSA, which reimburses only dental, vision, and preventive care. Because it doesn't cover general medical expenses, it doesn't disqualify you from HSA eligibility. If your employer offers one, it's the way to run both accounts: HSA for the long game, limited-purpose FSA for the crown and the glasses you know you're buying this year.

How to decide, in four questions

1. Is my health plan HSA-qualified for 2026? Check the deductible and the out-of-pocket maximum against the figures above. If no, the HSA isn't on the table and the question is only how much FSA to elect.
2. If yes, can I absorb the higher deductible in a bad year? The HSA is attached to a plan that leaves more risk with you. That's a cash-flow question, and it outranks the tax math.
3. What did I actually spend on health care last year? Pull the claims history from your insurer's portal. Elect the FSA against that number, not against a guess, and elect the amount you are confident you'll spend rather than the amount you might.
4. Does the plan have a grace period, a carryover, or neither? Ask HR in writing so you have the answer in an email.

And here's the thing not to do: don't elect a large health FSA in a year you're planning to switch to a high-deductible plan. A grace period running into January with money still in the account keeps you HSA-ineligible for the months it covers, and you will have paid for that mistake with the one tax-advantaged account that would have followed you for the rest of your life.