As someone who writes about retirement planning a lot, I'm well aware that I can't expect to live on Social Security alone once I decide to stop working (if I ever decide to stop working -- that's questionable).

Not only are Social Security cuts on the table, but I'm well aware that even a full set of benefits won't come close to replacing the income I'm used to earning. And while I do hope and plan to hold down a job in retirement, I certainly don't want to work as many hours as I do right now.

Given Social Security's limitations, I've been focused for many years on consistently funding a retirement savings plan. Since I'm self-employed, I contribute money to a solo 401(k), which is like a regular 401(k) except that it's managed by me, and I don't get the benefit of an employer match (boo).

A smiling person at a laptop.

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But there's another retirement plan my family got access to last year for the first time, and while it's not taking the place of my solo 401(k), I'm actually prioritizing contributions to it. And there's a big reason why.

It's my favorite plan for a reason

Oddly enough, my favorite retirement savings plan technically isn't a retirement plan. Rather, it's a health savings account, or HSA, whose purpose is to help people set aside funds for medical spending.

Eligibility to fund an HSA hinges on being enrolled in a high-deductible health insurance plan. Last year, my family's health coverage changed, which means we're now able to contribute money to an HSA. There's a reason I'm insistent on maxing that HSA out.

HSAs offer more tax benefits than any other tax-advantaged plan you'll find. Take my solo 401(k). I like and appreciate that it offers the benefit of tax-free contributions. Those lower my tax liability year after year.

HSAs offer that same benefit. But they also offer the benefit of being able to invest unused funds and enjoy tax-free gains, as well as tax-free withdrawals on money removed for medical spending.

Now you may be thinking, "How's an HSA going to help during your retirement?"

The answer is simple. I don't intend to touch my HSA until then. Instead, my family allocates extra money in our budget so we can not only max out our HSA, but also cover our healthcare costs as they arise. That way, we can invest our HSA for as long as possible and enjoy tax-free gains as our money (hopefully) grows.

Meanwhile, many seniors find that healthcare is their greatest monthly expense -- above housing, even. I do my best to take care of my health now (minus my tendency to sometimes eat cookies for dinner). But I have no idea what my healthcare expenses might amount to in retirement. So I want to have plenty of money set aside to cover them.

Plus, one lesser-known feature of HSAs is that once you reach age 65, you can take a withdrawal for any purpose without incurring a penalty. In that situation, you do face taxes on the money you remove. But that's why I think it's more than fair to call an HSA a retirement account, even though technically it isn't. Once you reach 65, it works just like a traditional IRA or 401(k) -- or a solo 401(k), if you have one like I do.

An opportunity you don't want to pass up

If you're able to contribute to an HSA, it pays to do so for the tax breaks involved. But more so than that, it pays to leave that money alone as long as possible to grow it into a larger sum.

Fidelity recently estimated that the average 65-year-old couple retiring in 2022 was looking at spending $315,000 in healthcare costs throughout their senior years. That's a pretty scary number. So if you're able to enter retirement with a large chunk of money socked away in an HSA, you're apt to experience that much less financial stress.