Two coworkers can earn the same salary, sign up for the same health plan, and still end up with wildly different bank balances by December.
The reason often comes down to one line on the benefits enrollment screen: FSA or HSA.
Both accounts let you pay for medical costs with pre-tax dollars, which sounds like the same deal.
The rules around deadlines, rollovers, and who qualifies are different enough that picking wrong can mean forfeiting hundreds or even thousands of dollars.
The FSA, or flexible spending account, is the classic use-it-or-lose-it arrangement.
You decide during open enrollment how much to set aside, and that money generally has to be spent by the end of the plan year.
Many employers offer a grace period or let you roll over a small amount — often around $640 — but anything beyond that typically goes back to your employer.
According to the benefits nonprofit KFF, workers forfeited an estimated hundreds of millions of dollars in FSA funds in recent years.
The HSA, or health savings account, flips the script.
It's only available if you're enrolled in a qualifying high-deductible health plan, but the money never expires.
It rolls over year after year, earns interest, and can be invested once your balance crosses a threshold your provider sets.
After age 65, you can withdraw funds for any purpose without the usual 20% penalty, though non-medical withdrawals are still taxed as income.
FSA contributions reduce your taxable income and cover medical costs, but you can't invest them.
HSA contributions are triple tax-advantaged: money goes in pre-tax, grows tax-free, and comes out tax-free for qualified medical expenses.
That's why personal finance types sometimes call it the "stealth IRA." The catch is the high-deductible requirement.
In 2025, an HSA-eligible plan must have a deductible of at least $1,650 for individual coverage, and out-of-pocket costs can't exceed $8,300.
If your employer offers a richer, lower-deductible plan, you may not be eligible for an HSA at all — no matter how much you'd like one.
If you expect predictable medical costs and your employer offers a traditional plan, an FSA can still work, especially if you're confident you'll spend the balance.
The trick is to estimate carefully rather than maxing it out.
Think about copays, prescriptions, dental cleanings, eyeglasses, and any planned procedures.
If you're generally healthy, can handle a higher deductible, and want a long-term savings vehicle, the HSA is usually the stronger play.
Contribute what you can, pay current medical bills out of pocket if your budget allows, and let the account grow.
Keep your receipts — you can reimburse yourself years later for old expenses, as long as you can document them.
One more thing: you can't contribute to an HSA if you're claimed as a dependent or enrolled in Medicare.
And if you have a spouse with a general-purpose healthcare FSA, that coverage can disqualify you from HSA contributions, even if the FSA isn't yours.
You can switch during open enrollment or after a qualifying life event like marriage, a new job, or a change in coverage.
My take: the HSA is the better deal for most people who can get one, largely because the money is yours forever.
But the FSA isn't a scam — it's just a bet that you'll spend what you set aside.
Final Thoughts
Make that bet with a real number, not a round one, because the only thing worse than a surprise medical bill is paying for one with money you already lost.