Elena had worked at her company for four years and every open enrollment season she picked the same thing: the FSA. She contributed $1,500 a year, used most of it on contacts and a couple of dentist visits, and didn't think about it much. Her mom had always used an FSA, so that's what she did.
Then, two years in a row, she lost money. Not a lot ($420 the first year, $380 the second) but enough to notice. The FSA's use-it-or-lose-it rule meant that any unspent balance at the end of the plan year vanished. Her company offered a $610 grace period carryover, but Elena's leftover amounts exceeded it both times.
A coworker named Diane, who had a chronic condition and had researched every benefit option extensively, asked Elena one day why she wasn't using the HSA instead.
"I didn't really know the difference," Elena admitted.
Here's the difference, and it's significant.
FSA: Use It or Lose It
A Flexible Spending Account lets you contribute pre-tax dollars, up to $3,300 in 2026, for medical expenses. The tax savings are real: every dollar you contribute avoids federal income tax, state income tax (in most states), and FICA. On a $2,000 contribution, that's roughly $600 in tax savings depending on your bracket.
The catch: unspent funds expire at the end of the plan year. Some employers offer a grace period (2.5 extra months) or a $640 carryover, but anything beyond that is gone. If you over-contribute and don't have enough qualifying expenses, you lose money.
HSA: The Triple Tax Advantage
A Health Savings Account is only available if you're enrolled in a high-deductible health plan (HDHP). The contribution limits are higher: $4,300 for individuals in 2026, $8,550 for families, and the tax treatment is extraordinary:
- Contributions are pre-tax (or tax-deductible if contributed outside payroll)
- Growth is tax-free: you can invest HSA funds in index funds, and gains are never taxed
- Withdrawals for qualified medical expenses are tax-free
That's a triple tax advantage: the only account in the US tax code that offers all three. And critically: the balance rolls over forever. There's no use-it-or-lose-it. Your HSA balance follows you even if you change jobs or retire.
What Elena Did
At the next open enrollment, Elena switched to her company's HDHP and opened an HSA. She contributed $3,000 in her first year, roughly the same as her old FSA contributions, and spent about $1,800 on medical expenses. The remaining $1,200 stayed in the account. She invested it in a target-date index fund.
By the end of year two, her HSA balance was over $3,800, growing tax-free while she paid for routine expenses out of pocket and let the invested portion compound.
"It's like a secret retirement account for medical expenses," Diane had told her. She was right. After age 65, HSA withdrawals for any purpose are taxed like a traditional IRA, no penalty. For medical expenses, they're still completely tax-free.
Use our Gross to Net Calculator to see how pre-tax HSA or FSA contributions affect your take-home pay. The paycheck impact is the same (both reduce your taxable income) but the long-term value of an HSA is dramatically higher if you can afford to let the balance grow.
When an FSA Still Makes Sense
If your employer doesn't offer an HDHP, you can't open an HSA. An FSA is your only option. FSAs also work well if you have predictable, high annual medical costs that you know you'll spend down completely. And dependent care FSAs (a separate type) allow up to $5,000 for childcare expenses, which can be a significant tax savings for parents.
But if you have the choice and your medical expenses are moderate or unpredictable, the HSA wins. Elena's only regret is that nobody explained this to her four years earlier.