Should I fund an HSA or a 401(k) first if I can't afford to max both?

A common order is: contribute enough to your 401(k) to capture the full employer match first, since that's an immediate guaranteed return. Then prioritize the HSA if you're on an HDHP, because it's the only triple-tax-advantaged account: contributions are pre-tax, growth is tax-free, and qualified medical withdrawals are tax-free. After maxing the HSA, return to the 401(k) and IRAs.

This works because everyone faces large medical costs eventually, and after 65 the HSA behaves like a traditional IRA for non-medical withdrawals. If your employer contributes to the HSA, grab that too. Model the trade-off with the Retirement Planner at wealthserene.com/tools/retirement-planner to see the long-run difference.