When it comes to saving for retirement, I now use two accounts: My 401(k) and a health-savings account.

Many people overlook HSAs as a retirement-savings vehicle because they are typically used to pay current medical bills. But these accounts, which Congress authorized in 2003, come with more tax advantages than 401(k)s and individual retirement accounts when used to cover medical costs—whether now or in retirement. And there are ways to use them to create tax-free income in retirement.

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