If you have the opportunity to contribute to both a 401(k) and a health savings account (HSA), you may wonder how best to take advantage of them. Determining how much to contribute to each type of plan will require some careful thought and strategic planning.

Understand the tax benefits

A traditional, non-Roth 401(k) allows you to save for retirement on a pre-tax basis, which means the money is deducted from your paycheck before taxes are assessed. The account then grows on a tax-deferred basis; you don't pay taxes on any contributions or earnings until you withdraw the money. Withdrawals are subject to ordinary income tax and a possible 10% penalty tax if made before you reach age 59½, unless an exception applies.

You can open and contribute to an HSA only if you are enrolled in a qualifying high-deductible health plan (HDHP), are not covered by someone else's plan, and cannot be claimed as a dependent by someone else. Although HDHP premiums are generally lower than other types of health insurance, the out-of-pocket costs could be much higher (until you reach the deductible). That's where HSAs come in. Similar to 401(k)s, they allow you to set aside money on a pre-tax or tax-deductible basis, and the money grows tax deferred.

However, HSAs offer an extra tax advantage: Funds used to pay qualified medical expenses can be withdrawn from the account tax-free. And you don't have to wait until a certain age to do so. That may be one reason why 68% of individuals in one survey viewed HSAs as a way to pay current medical bills rather than save for the future.¹ However, a closer look at HSAs reveals why they can add a new dimension to your retirement strategy.

HSAs: A deeper dive

Following are some of the reasons an HSA could be a good long-term, asset-building tool.

• With an HSA, there is no "use it or lose it" requirement, as there is with a flexible spending account (FSA); you can carry an HSA balance from one year to the next, allowing it to potentially grow over time.
• HSAs are portable. If you leave your employer for any reason, you can roll the money into another HSA.
• You typically have the opportunity to invest your HSA money in a variety of asset classes, similar to a 401(k) plan. (According to the Plan Sponsor Council of America, most HSAs require you to have at least $1,000 in the account before you can invest beyond cash alternatives.²)
• HSAs don't impose required minimum distributions at age 70½, unlike 401(k)s.
• You can use your HSA money to pay for certain health insurance costs in retirement, including Medicare premiums and copays, as well as long-term care insurance premiums (subject to certain limits).
• Prior to age 65, withdrawals used for nonqualified expenses are subject to income tax and a 20% penalty tax; however, after age 65, money used for nonqualified expenses will not be subject to the penalty [i.e., HSA dollars used for nonqualified expenses after age 65 receive the same tax treatment as traditional 401(k) withdrawals].

The bottom line is that if you don't need all of your HSA money to cover immediate health-care costs, it may provide an ideal opportunity to build a separate nest egg for your retirement health-care expenses. (It might be wise to keep any money needed to cover immediate or short-term medical expenses in relatively conservative investments.)

Additional points to consider

If you have the option to save in both a 401(k) and an HSA, ideally you would set aside the maximum amount in each type of account: in 2019, the limits are $19,000 (plus an additional $6,000 if you're 50 or older) in your 401(k) plan; $3,500 for individual coverage (or $7,000 for families, plus an additional $1,000 if you're 55 or older) in your HSA. Realistically, however, those amounts may be unattainable. So here are some important points to consider.

1) Estimate how much you spend out of pocket on your family's health care annually and set aside at least that much in your HSA.

2) If either your 401(k) or HSA — or both — offers an employer match, try to contribute at least enough to take full advantage of it. Not doing so is turning down free money.

3) Understand all HSA rules, both now and down the road. For example, you'll need to save receipts for all your medical expenses. And once you're enrolled in Medicare, you can no longer contribute to an HSA. Nor can you pay Medigap premiums with HSA dollars.

4) Compare investment options in both types of accounts. Examine the objectives, risk/return potential, and fees and expenses of all options before determining amounts to invest.

5) If your 401(k) offers a Roth account, you may want to factor its pros and cons into the equation as well.