If you are young and/or reasonably healthy, and working at a job that offers a Health Savings Account (HSA) with a high deductible plan, your order of tax sheltered savings should be: 1-401k up to the company match limit; 2-HSA up to the annual IRS limit; 3-overage in the 401k or a Roth, if you have extra cash. Some ACA plans are also HSA-compatible but the benefit is best with a large (possibly self-insured) corporate plan. I have $20K in my HSA, which I started in 2007, kept while I was on ACA and transferred to a new employer. The only health expense you cannot pay with it is the cost of insurance premiums, at least, not until you are nearing retirement age. You pay no tax on it, you take it with you from job to job, you don't have to spend it, and in one year you may have saved twice your deductible (depending on your plan) - and some plans allow you to invest a portion in mutual funds. Many of us will need major health care before retirement. HSA offers a cushion for that spend. As we are nearly guaranteed to need to spend on healthcare, this is tax-free assistance and a great nest egg. Many companies also contribute to the HSA on your behalf, annually; mine puts in the first $500.
