The short version
Compare plans by total yearly cost, not by premium: annual premium + your share of expected care, minus HSA tax savings and employer seed money. Four numbers per plan drive the whole decision — premium, deductible, out-of-pocket maximum, and HSA benefits — and the HSA side is where most people undercount the high-deductible plan by a thousand dollars or more.
Step 1: pull the four numbers for each plan
Every plan summary sheet has them, though sometimes buried: the annual premium (your per-paycheck amount times the number of pay periods), the deductible, the out-of-pocket maximum, and the coinsurance percentage. For a high-deductible plan, also note the employer's HSA seed money — free dollars your employer drops into your health savings account — and how much you plan to contribute yourself.
Step 2: estimate your year's medical spending
This is the only number you have to guess, so make it an educated one. Average your last two or three years of actual billed amounts — your insurer's explanation of benefits shows the full billed figure, not what you paid — then add anything already scheduled: a planned surgery, orthodontics, a birth, new ongoing prescriptions. Don't aim for one perfect number. You will run three versions of this comparison in Step 5: last year's number, your best guess, and a big year.
Step 3: compute your share of care under each plan
Your care share follows one rule: you pay the full bill up to the deductible, then your coinsurance percentage of the rest, and the out-of-pocket maximum caps the total. Say you expect $3,500 of care. On a plan with a $750 deductible and 20% coinsurance, you pay the first $750 plus 20% of the remaining $2,750 — that's $550 — for a care share of $1,300. On a high-deductible plan with a $3,500 deductible, the full $3,500 is yours. Simple, mechanical, no judgment calls.
Step 4: subtract the HSA benefits the premium hides
This is the step that changes the answer. HSA contributions are triple-tax-advantaged: pre-tax in, tax-free growth, tax-free withdrawals for medical expenses. A $2,500 contribution at the 22% bracket is $550 a year in tax savings — real money that belongs on the high-deductible plan's side of the ledger. Add the employer seed money on top: a $1,000 seed is $1,000 the PPO simply doesn't offer. Effective cost = premium + care share − tax savings − seed. Skip this step and the high-deductible plan looks roughly $1,550 worse than it is.
Step 5: run the worst case, then the range
Worst case needs no estimating: annual premium + out-of-pocket maximum is the most you can spend. The high-deductible plan's worst case is usually higher — that is the risk you are being paid to take through the lower premium. Then run the three spending versions from Step 2. The pattern you are looking for: the HDHP typically wins healthy years and loses nothing in catastrophic ones relative to its premium discount, while the PPO wins the steady moderate-use middle. If the PPO never wins any of the three versions, it is just the more expensive plan for you.
Worked example: a $3,600 HDHP against a $6,500 PPO
HDHP: $3,500 deductible, 20% coinsurance, $7,000 out-of-pocket max, $1,000 employer seed, $2,500 of your HSA contributions at the 22% bracket. PPO: $750 deductible, 20% coinsurance, $4,000 out-of-pocket max. Expected care: $3,500.
HDHP care share: the full $3,500 (deductible). Tax savings: 2,500 × 0.22 = $550. Effective cost = 3,600 + 3,500 − 550 − 1,000 = $5,550. PPO care share: 750 + 0.20 × 2,750 = $1,300; effective cost = 6,500 + 1,300 = $7,800.
The HDHP wins by $2,250 — a $2,900 premium gap plus $1,550 in HSA benefits against the PPO's $2,200 care-share advantage. In a $30,000 medical year, both plans hit their out-of-pocket caps and the HDHP still wins $9,050 to $10,500. In a $300 healthy year, the gap stretches to $4,450. The PPO's only realistic win is steady, moderate, copay-friendly use where the deductible gap dominates.
Run your own numbers
Use the open-enrollment comparison calculator to run your real plan numbers, including the low-use and big-year scenarios. Pair it with the take-home pay calculator if you want to see what the premium difference means per paycheck, and the emergency fund calculator to check whether your savings can absorb the HDHP's worst case.
Frequently asked questions
Should I really compare by total cost instead of premium?
Yes. The premium is guaranteed spending, but it is only half the story: a $2,900 cheaper premium with a high deductible can still lose if your care share runs $4,000 higher. Total yearly cost — premium + care share minus HSA benefits — is the only number that answers "which plan leaves me with more money."
How much does the employer HSA seed money actually matter?
Often a third of the HDHP's edge. In the worked example, the $1,000 seed plus $550 in tax savings totals $1,550 — without it, the HDHP's win shrinks from $2,250 to $700. Seed money is the HDHP's head start: a plan comparison that ignores it is comparing a race where one runner starts a second late.
What if I take prescriptions every month but never get hospitalized?
This is the moderate-use middle where PPOs often earn their premium back: copays cap each interaction cheaply while HDHP members pay full negotiated prices until the deductible. Check the prescription formulary too — drug tiers can differ between your employer's plans and matter more than the deductible for heavy prescription users.
Can I have an FSA and an HSA at the same time?
A general-purpose health FSA disqualifies HSA contributions for the whole year — the IRS treats it as coverage that pays before the deductible, which voids HSA eligibility. A limited-purpose FSA (dental and vision only) or a post-deductible FSA stays compatible. Picking the HDHP with an HSA and accidentally enrolling in a general FSA is one of the costliest open-enrollment mistakes.
What happens if I can't fund the HSA?
The math weakens but doesn't collapse: you lose your own contribution's tax savings, but the employer seed money still counts and the premium gap still applies. If cash flow is tight, even a small contribution is worth making — the tax break is proportional, and HSA dollars roll over forever, unlike FSA dollars.
Does this comparison work for family coverage?
The same method applies with family-tier numbers: family premium, family deductible, family out-of-pocket max, and the family's expected spending. One wrinkle: some family plans have embedded individual deductibles (each person's spending counts toward their own lower cap) while others are aggregate — check which your plan uses before estimating care shares.
Compare your actual plan numbers with the open-enrollment comparison calculator.