Starting in 2010, anyone can convert a traditional Individual Retirement Account to a Roth I.R.A. That’s great news for people who previously were shut out of a Roth because their adjusted gross income was more than $100,000.

Especially if you want to leave retirement assets to family or friends, a Roth conversion is one of the simplest, best planning tools available. You avoid the requirement to take yearly minimum distributions starting at age 70 1/2, and that can leave more for beneficiaries if you don’t use the money yourself. And subject to certain restrictions, no tax is assessed when the money is withdrawn, so income can compound tax-free.

But this technique has a hefty price tag. You owe income tax on the amount you convert, which can be the entire account balance or part of it. And some people worry about what might happen years from now if Congress eliminates the Roth.

One possibility is that those who have already converted will have their gains untaxed, said Christopher R. Hoyt, a professor at University of Missouri-Kansas City School of Law. Another is that only the investment earnings — not the amount converted — will then be taxable.

For now, many lawyers and financial advisers have put that thought aside and are strongly recommending Roth conversions to clients who can afford to pay the income tax. Yet this advice can be hard medicine to take, for it goes against the conventional wisdom that one shouldn’t pay a penny of tax sooner than necessary, and the idea of writing large checks to the Internal Revenue Service for an uncertain future