Q: I am 24 and just out of college, and I contribute to a traditional 401(k) at work. Now I find I can choose a Roth 401(k) instead of the traditional type. I believe I will be earning more money in the future, and I like the idea of giving the government money now and not later. But I realize that tax rules can change in the future, so I was thinking maybe I should stay with the traditional 401(k).

A: Like most investing questions, this boils down to making a bet on an unpredictable future. But instead of uncertainty about investment returns, inflation or interest rates, this involves tax policy.

With a traditional 401(k), you get a tax deduction on contributions, reducing your federal income tax bill every year you put money into the account. You pay no annual income tax or capital gains tax as the account grows, but all your withdrawals in retirement are taxed as income.

With a Roth 401(k), there is no tax deduction on contributions, so the Roth does not reduce your income tax during the years you put money into the account. But there’s no tax on annual growth or on withdrawals.

The Roth may be a better bet if you expect to be in a higher tax bracket when you withdraw money than you are when you put it in. This way, you pay tax at today’s relatively low rate to avoid tax at a higher rate later.

Factors such as inflation, expected rates of return and the number of years you have until retirement can affect this decision. Try the Roth vs. traditional 401(k) comparison calculator at www.fincalc.com to play with these variables.

But even with the best calculator, your question involves two uncertainties.

First, will your retirement income be bigger in retirement than it is today? Since you’re just starting out, the odds of that are pretty good.

Second, will the tax laws be the same when you retire as they are now?

They almost certainly will change – they change all the time. But I wouldn’t worry about it.

Congress could someday eliminate the Roth. But there’s no talk of that now, and tax-law changes are often accompanied by grandfather clauses that protect people who invested under the previous rules.

Tax rates, especially those for larger incomes, have been cut significantly since the start of the decade, and are now relatively low by recent standards. The federal government is running huge budget deficits and seems unable to reduce its spending, so I wouldn’t bet on further tax cuts.

So I think the best bet is to assume there won’t be any dramatic changes. If so, the Roth 401(k) is probably the better option for a young person with good earnings prospects and decades of investment growth to come.