The NUA Benefit and Optimal Investment in Company Stock in 401(K) Accounts

It is widely believed that contrary to standard asset allocation theory, employees irrationally hold concentrated investments in company stock in their 401(k) plans thus bearing firm-specific risk that could otherwise have been diversified away [See for example, Benartzi (2001)]. However, in measuring any such lack of diversification costs, a unique tax benefit associated with such investments (available to those who choose the Net Unrealized Appreciation [NUA] strategy) has been hitherto ignored. We analyze an employee's optimal allocation of retirement assets among alternative investments, including company stock, in the presence of the NUA tax benefit. The employee has a standard power utility function and seeks to maximize expected utility from her after-tax wealth upon retirement. Based on simulations, we find that, even when company stock is stochastically dominated by investments in the market index, the employee will allocate a non-trivial part of her retirement funds to company stock for a wide range of parameter values. Consistent with empirical evidence, the allocation to company stock is greater for employees closer to retirement and when the company's stock has experienced substantial gain in value