The HSA as a stealth retirement account: what maxing it out grows to

By DecisionSheet · Updated September 21, 2026 · 2026 tax figures

A health savings account (HSA) arrives in an enrollment packet as a way to pay this year's medical bills with untaxed money. Nothing in the rules requires it to be used that way. In the Employee Benefit Research Institute's database of accounts, 18% of holders had their HSA invested in something other than cash during 2024, and 56% of the accounts saw a distribution that year (EBRI).

This page runs the opposite case through the calculator: the 2026 self-only maximum of $4,400 paid in every year, invested at 7.5%, and never drawn on (open that scenario). After 30 years the projected balance is $489,079 — $132,000 contributed and $357,079 growth.

The three tax breaks, precisely

"Triple tax advantage" compresses three rules, and hides a condition on the third.

Going in, contributions are not taxed. A contribution the holder makes directly is deductible. One made by an employer, "including contributions made through a cafeteria plan" (Publication 969), may be excluded from gross income instead, and is "exempt from federal income tax withholding, social security tax, Medicare tax…" (Publication 15-B).

Inside, growth is not taxed. "An HSA is generally exempt from tax" (Publication 969). Interest, dividends and gains go unreported year by year.

Coming out, only medical withdrawals are untaxed. A distribution is tax free to the extent it pays or reimburses qualified medical expenses. Anything else is income, and "there is an additional 20% tax on the part of your distributions not used for qualified medical expenses" — with exceptions: "there is no additional tax on distributions made after the date you are disabled, reach age 65, or die" (Publication 969). From 65, a non-medical withdrawal is taxed as ordinary income and nothing more.

New money stops at Medicare: "no contributions can be made to an individual's HSA after they become enrolled in Medicare Part A or Part B" (Publication 15-B). Withdrawals are unaffected.

What the maximum grows to

Open this scenario

The arithmetic is not special to an HSA; it is what a fixed annual contribution does at a constant return. What is special is that no federal tax is taken out of the growth, or out of a withdrawal that pays a qualified medical expense. State rules can differ; California's do.

The chart's second line, cumulative premium savings, comes from the calculator's plan comparison and is not part of the balance.

Cash against invested

Set the assumed return to zero, changing nothing else, and the same $4,400 a year ends at $132,000 after 30 years — exactly what was paid in. Against $489,079 invested, the gap is $357,079 — the growth in the table's last row (the cash scenario).

Whether that gap is reachable is a question about the custodian, not tax law. The provider sets whether the account offers investments, whether a minimum must stay in cash, and what the fees are. None of it is modeled here, and every fee reduces the balance.

The fourth break: payroll deduction

The Social Security and Medicare exemption is not automatic: it belongs to contributions made through an employer's payroll under a Section 125 cafeteria plan.

In the model that is one checkbox. Through payroll the annual tax saving is $1,076: the 24% marginal rate entered plus 7.65% of Social Security and Medicare tax (Topic no. 751), on the $3,400 the holder puts in — the employer's $1,000 never appeared in taxable wages, so it is not shielded twice. Change that one input and the saving is $816: a difference of $260 a year, $7,800 across 30 years before any growth on it (the direct-contribution scenario).

Only up to the wage base, though: Social Security tax stops at $184,500 of 2026 wages (Publication 15), so a contribution out of wages above that saves the 1.45% Medicare portion alone. The model applies 7.65% at every income, overstating that advantage by 6.2% of the contribution.

The distinction is not hypothetical: partners and 2% shareholders of an S corporation "aren't eligible for salary reduction (pre-tax) contributions to an HSA" (Publication 15-B), and a top-up paid outside payroll is in the same position.

Paying out of pocket and reimbursing later

The projection assumes every medical bill is paid from money outside the account. The rules permit that, and permit reimbursement much later.

Notice 2004-50 is explicit: a holder "may defer to later taxable years distributions from HSAs to pay or reimburse qualified medical expenses incurred in the current year… Thus, there is no time limit on when the distribution must occur" (Notice 2004-50, Q&A-39).

Two conditions sit on that. The expense has to be incurred after the account was established — "expenses incurred before you establish your HSA aren't qualified medical expenses" (Publication 969). And the evidence has to survive: the holder "must keep records sufficient to show that" the distributions went exclusively to qualified medical expenses, that those "hadn't been previously paid or reimbursed from another source", and that they were not taken as an itemized deduction.

A third is not in the tax code: deferring reimbursement means carrying the medical bills out of cash flow for as long as it lasts. An account drawn on to pay them is the ordinary case, not the one this projection models.

Assumptions and limits

• The projection never withdraws anything: it assumes every medical bill is paid from other money. A dollar spent reduces the ending balance by that dollar and by the growth it would have earned.
• The contribution is held at $4,400 every year in nominal dollars. The IRS limit is inflation-adjusted (Rev. Proc. 2025-19), and a holder aged 55 or over may add $1,000 (Publication 15-B). Neither is modeled.
• The employer's $1,000 counts inside the $4,400, as the limit requires, so the holder's own share is $3,400. The projection invests the whole $4,400.
• The return is a constant 7.5% every year, with no losing years and no fees — an assumption, not a forecast.
• Balances are nominal. As an illustration only, at an assumed 2.5% inflation the $489,079 at year 30 would buy what $233,165 buys today. That rate is chosen here; the calculator does not model inflation.
• 30 unbroken years of contributions assume as many years of eligibility: high-deductible health plan coverage, no other disqualifying coverage, no Medicare, not someone else's dependent (Publication 969). The calculator checks none of it.
• State income tax need not follow the federal rules. California does not conform: contributions are not deductible there, and "all interest earned and any taxable dividends earned on HSAs are taxable in the year earned" (FTB Publication 1001, page 9). The calculator takes one combined federal-plus-state rate and cannot represent a state that diverges.
• Self-only figures throughout; the 2026 family limit is $8,750.

Method and sources

The model is calculateHsaVsPpo in the HSA vs. PPO calculator. Its projection starts from a zero balance and, each year, adds $4,400 and then applies the 7.5% return to the whole balance including that year's contribution; it never withdraws. The annual tax saving is the marginal rate, plus 7.65% for a payroll contribution, applied to the holder's own $3,400.

• Rev. Proc. 2025-19 — the 2026 HSA limits, $4,400 self-only and $8,750 family.
• Publication 969 — eligibility, the exemption on the account, the 20% additional tax and its exceptions, and the recordkeeping rules.
• Publication 15-B — the payroll tax exemption, the age-55 catch-up, the Medicare cut-off, and salary reduction for partners and S corporation shareholders.
• Notice 2004-50, Q&A-39 — no time limit on a reimbursing distribution.
• Topic no. 751 — the 6.2% Social Security and 1.45% Medicare employee rates behind 7.65%.
• Publication 15 — the 2026 Social Security wage base of $184,500, above which the 6.2% stops.
• FTB Publication 1001 — California's non-conformity.
• EBRI HSA Database, 2024 — the share of accounts invested and the share taking distributions.

Open this scenario in the calculator

All figures on this page come from the HSA vs. PPO calculator. Change any input there and the numbers update.