Is a Roth 401(k) preferable to a traditional 401(k)? Generally, that depends on tax rates and whether you prefer to pay taxes as you contribute in your working years or as you withdraw funds in retirement.
Roth 401(k) plans are created with after-tax funds, while traditional 401(k) plans are funded through pre-tax dollars. By choosing a Roth 401(k) and paying your taxes upfront, the savings in your account grow tax-free, and once you have held the account for at least five years and are past age 59-½, your withdrawals are also tax-free. Withdrawals from traditional 401(k) plans are taxed as ordinary income upon retirement.
Harvard Business School researchers found that Roth 401(k) accounts produce greater purchasing power in retirement than traditional 401(k) programs because of basic human nature – people's tendency to use rules of thumb when determining their retirement contributions.
Contributions are often made in terms of percentages or dollar targets, and a flat savings rate makes a huge difference when considering pre-tax vs. post-tax dollars. Let's assume that you are maxing out your 401(k) at the current limit of $18,000 annually (and that you haven't reached age fifty yet to allow a $6,000 catch-up contribution). With a Roth 401(k), that $18,000 contribution will still be worth $18,000 at retirement. With a traditional 401(k), that $18,000 contribution is only worth $18,000 minus whatever tax rate applies at retirement.
To think about it another way: If you are contributing $18,000 to a Roth 401(k), you are indirectly contributing more than $18,000 toward your retirement because you are also paying the taxes on those funds in that same year.
This advantage could be partially neutralized by future tax rates. If you are in a high tax bracket now, your tax bracket in retirement is likely to be significantly lower – thus the taxes you pay now by contributing to a Roth 401(k) are greater than the taxes you will pay upon withdrawal.
Lead study author John Beshears gives the following example in an interview with the Wall Street Journal: Assume an annual $5,000 contribution to a 401(k) for forty years until retirement, with a 5% return. The balance will be $600,000 at retirement. At a 20% tax rate – not unreasonable upon retirement – the spending power is reduced to $480,000. With a Roth 401(k), the spending power of that nest egg is still $600,000.
While the Harvard study finds that Roth 401(k)s tend to result in greater purchasing power, that doesn't mean that you should dismiss a traditional 401(k). If you are maxing out your 401(k), a Roth is clearly a better choice – but otherwise, you can simply adjust the contribution amount to a traditional 401(k) upward to account for anticipated taxes at retirement, and gain the further tax advantage of lowering your taxable income during your working years.
Depending on your employer's plan, you may be able to hedge your bets. Some employer plans allow you to have a traditional 401(k) and a Roth 401(k) simultaneously – but your total contributions are still capped at the annual limit. You may be able to alternate annual contributions between the two accounts, or possibly divert an annual percentage to each account.
The cost/benefit calculations are not straightforward and require some assumptions on growth, inflation, and tax rates. We advise running scenarios on your preferred retirement scenarios using online calculators – or, better still, seek the advice of a financial professional who can address your retirement goals and lay out your best options in an understandable way.