Among the most important decisions investors make is their choice of location for assets within the various alternatives available for retirement (tax-advantaged) accounts. Allocating between a traditional IRA (a pretax, tax-deferred account) and a Roth IRA (a post-tax, tax-free account) can have a pronounced impact on retirement outcomes, given the $14 trillion in tax-advantaged retirement account assets at the end of 2015.
David Brown, Scott Cederburg and Michael O’Doherty contribute to the literature on retirement asset location with their June 2016 paper, “Tax Uncertainty and Retirement Savings Diversification.”
The modeling approach they adopt accounted for investor age, current income and taxable income from outside sources in retirement, as well as the highly progressive income tax regime now in place. The authors point out that “the marginal rate for a single taxpayer with inflation-adjusted income of $100,000, for example, has changed 39 times since the introduction of income taxes in 1913 and has ranged from 1% to 43%.” This creates considerable uncertainty.
Because risk-averse investors (and most investors are risk averse; it’s generally only a matter of degree) dislike uncertainty, this should create a preference for Roth accounts, as they “lock in” the current rate, eliminating the uncertainty associated with future changes.
On the other hand, a traditional account, which offers retirement savers the benefit of deducting current contributions, allows investors to “manage their current taxable income around tax-bracket cutoffs, which is valuable under a progressive structure.”
Another benefit of traditional accounts, the authors write, is that “the progressive tax rates faced in retirement provide a natural hedge against investment performance. Investors with poor investment results and little wealth in retirement will pay a relatively low marginal tax rate, whereas larger tax burdens are borne by investors who become wealthy as a result of good investment performance.” This creates tension between the traditional and Roth options.