When it comes to saving for retirement, most people focus on accounts like 401(k)s. And there's a good reason for that.

With a traditional 401(k), you get a tax break on the money you contribute toward retirement. You also get to enjoy tax-deferred investment gains. With a Roth 401(k), investment gains are tax-free, as are withdrawals.

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Plus, 401(k)s tend to be pretty easy to fund. Many companies offer them, and once you sign up, your contributions are taken as automatic deductions from your paychecks.

But there's another type of account that doesn't always get the attention it deserves in the context of retirement savings -- a health savings account, or HSA.

At first, an HSA might seem like a niche tool for covering healthcare expenses. After all, it's right there in the name. But actually, when used strategically, you may find that an HSA is even more powerful than a 401(k) for your retirement.

Why HSAs beat 401(k)s

It's true that 401(k)s offer a number of tax benefits. But HSAs are unique in that they combine the tax breaks offered by traditional and Roth 401(k)s.

With an HSA:

• Contributions go in tax-free
• Investment gains are tax-free
• Withdrawals are tax-free as long as they're used for qualifying medical expenses

That's a pretty winning combination.

Now you may be thinking, "Well, those are some nice tax breaks, but you can only use an HSA for medical expenses." But that's where you're wrong.

It's true that non-medical HSA withdrawals can incur a penalty -- but only if you're under 65. Once you turn 65, you can use an HSA for any purpose without being penalized. This allows your HSA to serve as a backup retirement account.

Of course, you might need the bulk of your HSA to cover healthcare expenses in retirement. But if you have money left over, rest assured that it won't have to go to waste or become subject to penalties.

If you use your HSA for non-medical withdrawals at or after turning 65, your withdrawals will be subject to taxes. That's the one hiccup. But in that case, you're in no worse a position than with a traditional 401(k).

Don't write off an HSA for your retirement

You might assume that when it comes to saving for retirement, a 401(k) is your best bet. But you may want to incorporate an HSA into your savings plans if your health insurance plan is compatible with one. It could end up serving a few important purposes in retirement -- giving you access to tax-free funds for healthcare expenses, and providing income to cover expenses your 401(k) can't.