How to Use an HSA to Save a Lot

It’s possible to amass $1 million in special health savings accounts to use in retirement, a new analysis finds, with several big caveats.

You have to start young, contribute the maximum each year and leave the money untouched for decades instead of spending it on medical needs.

Health savings accounts, known as H.S.A.s, let people set aside pretax money for health and medical care.

To open an H.S.A., you must have a specific type of health plan with a high deductible — an amount you must cover out of pocket before insurance pays. The money can be saved or invested to grow tax-free, and is tax-free when withdrawn and spent on eligible care or products. (The federal government does not tax the accounts, but some states assess state taxes.)

Because of their robust tax advantages, H.S.A.s are seen as a valuable tool to save for health needs later in life, including costs that aren’t covered by Medicare, the federal health plan for older Americans. H.S.A. funds can also be spent on nonmedical costs after age 65 without penalty. The money is taxed as ordinary income.

The new analysis by the Employee Benefit Research Institute, a nonprofit group, assumes that at age 25, a saver begins contributing the maximum allowable amount each year ($4,300 for an individual in 2025 — the amount is tweaked annually for inflation — and an additional $1,000 for people 55 and older) and continues those contributions through age 64 with no withdrawals, “regardless of whether the individual uses any health care services.” It also assumes the funds are invested and earn a 7.5 percent rate of return.