The HDHP-versus-traditional-plan decision comes down to one calculation, not a rule of thumb. Here is the arithmetic with 2027 numbers, plus the eligibility traps that disqualify people after they have already enrolled.
Open enrollment is the only moment each year when the HSA decision is actually made. Everything else — investing it, reimbursing yourself, the shoebox strategy — depends on a choice you make in a benefits portal in about twenty minutes, usually while comparing two plans that are described in language designed to make comparison hard.
The advice that circulates at this time of year is mostly a rule of thumb: young and healthy, take the HDHP; family with medical needs, take the PPO. That heuristic is wrong often enough to be expensive, because it ignores the two variables that usually decide the outcome — the premium gap and the employer's HSA contribution.
Here is the actual calculation, with 2027 numbers.
Do not compare deductibles. Compare total annual cost under each plan:
Premiums for the year + what you realistically spend out of pocket − the tax you save on HSA contributions − what your employer puts into the HSA = your real cost
Four terms. The first is certain, the second is a forecast, and the last two are the ones people leave out — which is why the HDHP usually looks worse than it is.
Take the annual premium for each plan straight from your enrollment materials — per paycheck, multiplied by the number of paychecks.
This is the only figure in the whole comparison you know with certainty on enrollment day. Everything else depends on what happens to your health over twelve months. So the premium gap deserves more weight than it usually gets: it is money you either spend or keep, regardless of whether you get sick.
A typical HDHP saves somewhere between $600 and $2,500 a year in premiums for family coverage. That saving is banked on day one.
Do not model your average year. Model two:
The bad-year column is the one that matters for peace of mind, and it is where the comparison often surprises people: a high-deductible plan with a low out-of-pocket maximum can have a better worst case than a low-deductible plan with a high one. The deductible tells you when coverage starts; the out-of-pocket maximum tells you how bad it can get. Only the second one caps your risk.
HSA contributions avoid federal income tax, and — when made through payroll deduction — also FICA, which is 7.65% that no 401(k) contribution escapes. That payroll-deduction detail is worth getting right: contributing directly to an HSA and deducting it on your return saves the income tax but not the FICA.
For 2027 you can contribute $4,500 self-only or $9,000 family, plus $1,000 if you are 55 or older.
At a 24% federal marginal rate, a family contributing the full $9,000 through payroll saves roughly $2,160 in federal income tax plus about $689 in FICA — call it $2,850, before any state tax. That is not a rounding error; on many comparisons it is larger than the entire premium difference.
Two cautions. If you will not actually contribute the maximum, use the number you will really contribute. And if you live in California or New Jersey, your state does not recognise HSAs, so the state portion of the saving does not apply — see HSA state taxes in California and New Jersey.
Many employers seed the HSA — commonly $500 to $1,500 — and often only on the HDHP. It is yours immediately, it is not taxed, and it does not count against you if you leave.
Subtract it directly. An employer contribution frequently closes the entire gap on its own, and it is the single most common omission when people run this comparison.
Family coverage, 24% marginal federal rate, employer contributes $1,000 to the HSA on the HDHP only. The family contributes the full $9,000.
| Traditional PPO | HDHP + HSA | |
|---|---|---|
| Annual premium | $6,000 | $4,200 |
| Realistic out-of-pocket (quiet year) | $1,500 | $3,200 |
| Tax saving on HSA contribution | $0 | −$2,850 |
| Employer HSA contribution | $0 | −$1,000 |
| Net cost, quiet year | $7,500 | $3,550 |
Now the bad year — both plans reach their out-of-pocket maximum:
| Traditional PPO | HDHP + HSA | |
|---|---|---|
| Annual premium | $6,000 | $4,200 |
| Out-of-pocket maximum | $9,000 | $10,000 |
| Tax saving + employer contribution | $0 | −$3,850 |
| Net cost, bad year | $15,000 | $10,350 |
The HDHP wins both columns here — and note why. It is not the deductible. It is the premium gap plus the tax treatment plus the employer money, which together outweigh a worse raw out-of-pocket maximum.
Change the inputs and the answer changes. Drop the employer contribution to zero, assume the family only contributes $3,000, and narrow the premium gap to $600, and the PPO wins the quiet year comfortably. That is the point: this is arithmetic, not a personality type. Run it with your own four numbers.
Getting the arithmetic right is useless if you are not eligible to contribute. These are the ways people discover, in March, that they should not have been.
To be HSA-qualified in 2027 a plan must have a deductible of at least $1,750 self-only or $3,500 family. Both rose from 2026.
This is the trap that requires no action on your part to spring: if your employer keeps the same plan design with a deductible that sat just above the 2026 floor, it can fall below the 2027 floor. The plan stops being HSA-qualified, and anything you contribute becomes an excess contribution subject to a 6% penalty for every year it stays in the account. Check the deductible against the 2027 floor before you elect, not after. If it has already happened, how to fix excess HSA contributions covers the correction.
A general-purpose health FSA — yours or your spouse's — makes you ineligible to contribute to an HSA, because an FSA can reimburse your expenses from the first dollar, which is exactly what disqualifying coverage means.
Couples enrol separately and often never compare elections, so this one is common and genuinely invisible until a tax preparer finds it. A limited-purpose FSA (dental and vision only) is fine and can be worth having alongside an HSA.
Enrolling in any part of Medicare ends HSA eligibility. The detail that catches people: Part A enrolment is retroactive up to six months when you sign up after 65. Contributions made during that retroactive window become excess contributions after the fact. If you are approaching 65 and still working, stop contributing six months before you intend to enrol — HSA after age 65 goes through the timing.
If you are HSA-eligible on December 1, 2027, the last-month rule lets you contribute the full annual maximum for 2027 even if you were only eligible for part of it.
The catch is the testing period: you must stay HSA-eligible through the end of 2028. Break it — by switching to a non-qualifying plan, or enrolling in Medicare — and the extra contributions become taxable income plus a 10% penalty. It is a genuinely useful rule for anyone starting an HDHP mid-year, and a trap for anyone who expects to retire or change coverage the following year.
Two 2026 rule changes widened eligibility and are still not widely understood, so they are worth re-checking at this enrollment:
Both are covered in the 2026 HSA rule changes.
The HDHP question is not "am I healthy?" It is:
Premium gap + tax saving + employer contribution — is that more than the extra out-of-pocket exposure I am taking on?
For a lot of people it is, by more than they expect, because three of those four terms get left out of the mental version of the comparison. For some people it is not. The only way to know is to put your own numbers in the table.
And once you are enrolled, the decision that compounds is what you do with the account — see should you invest your HSA and the shoebox strategy.
This is general information, not tax or benefits advice. Plan designs vary and the eligibility rules have edge cases — confirm against your own plan documents and, where the numbers are large, with a tax professional.