Unlike traditional 401(k)s and I.R.A.s, Roth I.R.A.s and Roth savings options within workplace plans are funded with after-tax dollars — in other words, you pay the income tax bill upfront. Like a traditional 401(k) or I.R.A., your investments grow tax-free. Unlike tax-deferred accounts, Roth withdrawals are generally tax-free too, if used as intended in retirement or by your heirs.

Roths also offer a way to hedge your bets against possible higher tax rates in the future, said Ed Slott, a tax expert and Roth guru.

“Most older people are heavily overweighted in tax-deferred accounts — they have no tax risk diversification,” Mr. Slott said. “These are sophisticated investors who would never put all their eggs in one basket, because that’s a basic rule of investing — yet all their eggs are in one tax basket, so they’re at the mercy of a possible future higher tax bill.”