The GAO reports that the federal government expects to forgo an estimated $17.5 billion in tax revenue from IRAs in 2014. For tax year 2011 (the most recent year available), an estimated 43 million taxpayers had IRAs with a total reported fair market value of $5.2 trillion. Of those taxpayers, 99% had aggregate IRA balances (including inherited IRAs) of $1 million or less.

The GAO says generally, taxpayers with IRA balances of $5 million or more tend to be joint-filers that are higher wage earners and over the age of 65. Accumulating an IRA balance over $5 million usually requires large employee and employer contributions sustained over decades, supplemented by additional rollovers from an employer-sponsored retirement plan, the GAO suggests.

There is no statutory limit on IRA accumulations or rollovers from employer defined contribution plans, the GAO notes. However, Congress has limited annual contributions to IRAs in order to prevent the excessive tax-favored accumulation of unduly large balances.

The GAO developed multiple scenarios to illustrate how much a person could have contributed given statutory limits on contributions from 1975 to 2011. First, GAO researchers calculated hypothetical accumulations using historical stock and bond market returns. Additionally, researchers calculated the IRA accumulation assuming the nominal historical interest rates as reported in the Social Security Trustees reports. Using these analyses, the GAO report says an individual who made the maximum contributions every year since 1975 to a traditional IRA could have accumulated about $303,000.

IRA rollover rulemaking continues to be a topic of concern and discussion for many different regulators in the retirement plan industry. The GAO says it is not making recommendations at this time, but will release a separate report with its final results on individual retirement accounts later this year. The full IRA report can be downloaded here.