In our post from last week, we highlighted the potential benefit of converting tax-deferred assets to a Roth IRA. We showed that the amount of tax alpha, or the amount of additional return realized from converting, depended on current versus future tax rates. However, we simplified how a retiree may fund the tax liability by using retirement assets. In this post, we show the additional tax alpha when funding Roth conversions without using tax-deferred assets.
Funding Roth Conversions Using Assets in a Taxable Account
The additional tax-alpha from using taxable account assets arises due to these assets no longer generating taxable interest and dividends owed each year. Instead, a retiree could use these assets to pay for funding Roth conversions. Consequently, the benefit of funding Roth conversions with taxable account assets grows over time. But, two additional complexities arise. The return on the underlying asset is the first. The ultimate intended use of the taxable account assets is the second complexity. Markets dictate the first complexity, but not the second.
So, we may not know how the stock and bond market will perform in the future. But, a retiree may know whether they will use taxable assets to supplement their retirement income needs. If taxable assets are used to supplement retirement income and/or for funding Roth conversions, then there will likely be a long-term capital gain that would reduce the tax alpha. Otherwise, taxable assets may pass to an heir with a step-up in cost basis, thereby eliminating the capital gain tax owed by the retiree.
Case Study Results from Over 20 Years
To help quantify the additional tax alpha, we revisited the analysis in the Roth (2020) article for a 20-year period. We added the two complexities mentioned above, that the tax alpha will depend on market returns and if the taxable account assets received the step-up in cost basis. The left panel below shows the tax alpha without the step-up included. The right panel shows tax alpha when the step-up occurs.
Key Insights from funding Roth conversions
The results above indicate the importance of the step-up in cost basis on the tax efficiency of funding Roth conversions. The horizontal axis represents the fraction of the cost basis of the taxable account assets used. So, using current interest, dividends or available cash from a taxable account implies a cost basis equal to 1, and highly appreciated assets would have a value approaching 0.
- From the left pane, the tax alpha ranges from 0.10% to 0.30% per year over twenty years. Lower (higher) tax alpha occurs when markets underperform (overperform) their historical average returns.
- When the heir realizes the tax-efficient step-up in cost basis, the tax alpha is up to 0.10% per year over twenty years. Also, the breakeven for this additional tax alpha occurs at approximately 0.70, implying that a highly appreciated asset intended for an heir should not be used for funding Roth conversions.