The FSA-vs-HSA decision usually is not a choice at all — your health plan generally dictates which one you are eligible for, so the real question is how much to fund. FSA and HSA sound similar — both are pre-tax accounts for medical expenses — but they are structured for very different purposes: an HSA rolls over indefinitely, can be invested, and follows you between jobs, while an FSA is generally use-it-or-lose-it within the plan year. The specifics depend on your plan and situation, and these rules and figures can change.
What is the core difference between an FSA and an HSA?
HSA (Health Savings Account): Per IRS Publication 969, an HSA is generally available only alongside an HDHP. Funds generally roll over indefinitely, can be invested, and follow you between jobs. The IRS describes a triple tax advantage — generally deductible going in, tax-free growth, and tax-free for qualified medical expenses. After age 65, the IRS generally lets you withdraw for any reason (paying ordinary income tax on non-medical use, much like a traditional IRA).
FSA (Flexible Spending Account): Generally available with most non-HDHP plans. The IRS rules generally require funds to be spent within the plan year, though some plans allow a small carryover or grace period. An FSA generally doesn't follow you between jobs — many people who leave a company forfeit unused funds. Your plan's specific terms may differ.
What are the contribution limits and eligibility thresholds?
The IRS sets dollar limits on both accounts and re-indexes most of them year to year — so the useful move is to learn which limits apply to you, then confirm the current figure at the source rather than trusting a number you saw last year. This guide deliberately doesn't print the dollar amounts for that reason.
- HSA contribution limit — the IRS sets separate annual maximums for self-only vs family HDHP coverage, plus an additional catch-up amount once you reach the qualifying age (commonly cited as 55+). Employer contributions count toward the same limit. Current-year figures are in IRS Publication 969.
- HDHP eligibility thresholds — an HSA is only available alongside a plan the IRS classifies as a High-Deductible Health Plan, meaning a minimum deductible and a capped maximum out-of-pocket within IRS-set bounds. Your plan documents (or HR) confirm whether the plan qualifies; the threshold numbers themselves come from the IRS each year.
- Health FSA contribution limit — the IRS caps annual health-FSA salary-reduction contributions, separate from the HSA. A Dependent Care FSA has its own, different cap. Both are set by the IRS / your plan.
- Limited-Purpose FSA cap — generally follows the health-FSA limit (see the section below); confirm the current amount with your plan.
- Carryover vs grace period — for health FSAs the IRS permits either a limited carryover of unused funds into the next year or a short grace period to spend them, not both, and only if your plan opts in. The carryover dollar cap is re-indexed periodically — confirm the current amount and which option your plan offers.
- State tax treatment — a few states tax HSA contributions at the state level even though they're federally pre-tax (California and New Jersey are the commonly-cited examples). If you're in one, the HSA's tax advantage is federal-only for you — worth checking your state's current treatment.
When should you fund the HSA aggressively?
Some people lean into the HSA when:
- They have an HDHP and can pay current medical bills out of pocket.
- They want to invest the HSA balance for retirement (most administrators offer brokerage-style investing once you hit a minimum balance).
- Their employer contributes — that money is essentially a bonus.
- They're young and healthy and want decades of tax-free growth.
A strategy many people use, when cash flow allows: max the HSA and pay current medical bills with after-tax money, keeping receipts. Because the IRS generally places no deadline on HSA reimbursements, decades later you can reimburse yourself tax-free from the HSA — turning it into a stealth retirement account. Whether this fits depends on your situation.
When should you fund the FSA conservatively?
Other people keep the FSA modest when:
- They have predictable medical spend: prescription refills, planned dental work, glasses, copays.
- They have a Dependent Care FSA option and kids in daycare — many people fund this close to the cap, since it's often a clean win.
- They can estimate their spend within ~$200. The IRS generally lets you carry over a small amount (currently around $640, but it often helps to check the current year), and amounts beyond that are typically forfeited.
A common rule of thumb: many people estimate their floor — the spend they're confident will happen — and fund that, rather than guessing high.
What is a Limited-Purpose FSA — and can you have both?
If you have an HSA but also expect predictable dental and vision spend, your employer may offer a Limited-Purpose FSA. Per IRS rules, this generally lets you pay dental and vision costs with FSA dollars while keeping the HSA growing for medical expenses — two pre-tax buckets, no conflict. Plan availability varies, so it often helps to confirm with HR.
What should you ask HR?
- Does the FSA have a grace period or carryover provision?
- If I have an HSA, can I also enroll in a Limited-Purpose FSA?
- Does the employer contribute to the HSA, and when does the contribution land?
- What's the deadline to submit FSA reimbursement claims for the plan year?
The IRS publishes detailed rules on both account types — IRS Publication 969 (HSA, HRA, FSA, and MSA rules) (affiliate link — OffbookHR may earn a commission if you buy through this link. It does not affect ranking.). For which costs the IRS treats as qualified medical expenses, many people also check IRS Publication 502 (Medical and Dental Expenses) (affiliate link — OffbookHR may earn a commission if you buy through this link. It does not affect ranking.). Because these thresholds and figures can change, it often helps to confirm the current rules at the source for your situation.