Every November, millions of Americans stare at a benefits portal and pick the account with the friendlier acronym.
That snap decision can be worth hundreds — sometimes thousands — of dollars a year, and most people never run the math.
An FSA, or flexible spending account, is use-it-or-lose-it.
You decide during open enrollment how much to set aside, and in most cases you have to spend that money by December 31 or forfeit whatever is left.
Some employers offer a grace period until March 15 or let you carry over a small amount — for 2025, the carryover cap is $640 — but that's up to your plan, not you.
An HSA, or health savings account, works differently.
You can only open one if you're enrolled in a high-deductible health plan, but the money never expires.
It rolls over year after year, earns interest or investment returns if you choose, and comes out tax-free for qualified medical costs at any point in your life.
Both accounts let you contribute pre-tax dollars, and both let you withdraw tax-free for qualified expenses.
The HSA adds a third break: once you hit 65, you can pull money out for anything, not just medical bills, and pay ordinary income tax like a traditional IRA.
No other account in the tax code gets that triple treatment.
For 2025, HSA contribution limits are $4,300 for self-only coverage and $8,550 for family coverage, with an extra $1,000 catch-up if you're 55 or older.
FSA limits are $3,300 per employee, and your employer can add up to $660 more.
Because it's the only option if your workplace offers a traditional PPO or HMO instead of a high-deductible plan.
And if you have a predictable, recurring expense — think glasses, contacts, therapy, or a kid's braces — an FSA can be the cleaner move, since you don't have to worry about whether your plan qualifies.
The average worker forfeits somewhere between $50 and $100 a year, but the people who get burned are the ones who guess $2,500 and spend $900.
Before you type a number into that box, pull up last year's receipts.
Look at what you actually paid out of pocket for dental, vision, prescriptions, and copays.
That total — not your best guess — is your starting point.
One more thing worth knowing: if you leave your job mid-year, your FSA usually dies with the plan unless you elect COBRA coverage for it.
Your HSA is yours forever, even if you change employers or insurers, and you can keep contributing to it on your own if you stay in a qualifying plan.
If you're healthy, have savings to cover a higher deductible, and want an account that grows instead of evaporating, the HSA is usually the better long-term play — and you can invest the balance rather than leaving it in cash.
If you're on a traditional plan or you know exactly what you'll spend next year, the FSA still does its job.
Just treat the number you enter like a budget, not a wish.
My honest opinion: the FSA gets picked because it's simpler to explain in a benefits meeting, not because it's better for most people.
Final Thoughts
Run your own numbers before the enrollment window closes, because nobody at HR will do it for you.