If you have access to a high-deductible health insurance plan, you may be familiar with health savings accounts. While they seem to be a medically-focused vehicle, they can actually serve as a “best of both worlds” retirement account.

The way a health savings account, or HSA, works is that you’re eligible to contribute a certain amount of pre-tax funds to cover health-related expenses. If you have the HSA through your job, your employer may even make contributions on your behalf.

The funds in this account are eligible to be withdrawn for anything on the long list of eligible health-related expenses. So even if this is all you do with the account, the pre-tax nature of your HSA contribution means you’ve already saved money.

But where HSAs deliver a significant punch is that you don’t have to withdraw your funds anytime soon, allowing you to accumulate them. And since some HSAs allow you to invest your funds, you can grow your balance just like you would an IRA account. Indeed, not only are HSA contributions tax-free, but so is their growth.

There’s even a third tax benefit: so long as the funds are for an eligible expense, you can withdraw any amount tax-free.

Because you can do this at any future date for a documented expense incurred while you had the plan, this means you can save the money until you’re retired, and then withdraw tax-free funds as you like based on past expenses.

Though it requires a little bit of recordkeeping, HSAs can serve as the ultimate retirement account, combining the strengths of traditional and Roth IRAs. Like a traditional IRA, you can claim a tax deduction upon contributing, while like a Roth, you can withdraw the funds tax-free. And like both accounts, all the growth goes untaxed as well.