Rationale for lower deduction limits for married couples filing separately?

Question

I recently discovered that I can't contribute to a Roth IRA if I file taxes separately from my wife. What is the rationale for this rule?

mod edit http://money.cnn.com/retirement/guide/IRA_Roth.moneymag/index4.htm

Roth IRA contributions are limited by income level. In general, you can contribute to a Roth IRA if you have taxable income and your modified adjusted gross income is either:

• less than $167,000 if you are married filing jointly
• less than $105,000 if you are single, head of household, or married filing separately (if you did not live with your spouse at any time during the previous year)
• less than $10,000 if you're married filing separately and you lived with your spouse at any time during the previous year.

...

Answer 1

From the Joint Committee on Taxation's General Explanation Of The Tax Reform Act of 1986, page 220:

Congress concluded that rules that encourage filing separate returns give rise to unnecessary complexity and place an unwarranted burden on the administration of the tax system.

Although this section of the document is not about IRAs, this act altered the IRA contribution rules among other things, and that statement appears to be the general philosophy: the government just doesn't like married couples filing separately, and essentially tries to punish them for doing so. Note that the same income limit applies for deductible contributions to Traditional IRAs, if either spouse is covered by an employer-provided plan (see here).

This page suggests one such incentive for the IRA in particular: "The rationale: the government doesn't want to give you a tax break in case your spouse is high-income". If one spouse is earning a lot -- for instance, over the Roth IRA limit -- and the spouses are living together, the other spouse is presumably reaping some of the benefits of those high earnings, so should not be allowed to benefit from the Roth, which is supposed to be unavailable to high earners. Also, if one spouse had earnings over the Roth IRA limit, they could possibly use financial sleight-of-hand to shift some of the income to the other spouse, thus enabling both to contribute.

I don't see that these reasons really justify the drastic nature of the penalty, but I think that's about as much logic as we can hope for in the tax code.

Answer 2

I'm not sure. IRAs were meant to supplement retirement, and intentionally excluded high wage earners. But the restriction on people who file separately actually allows some families to skirt this issue. For example, let's say the household income is $500,000 a year. If the husband makes $250,000, and the wife makes $250,000, neither one can contribute to an IRA, whether they file jointly or separately. However, if the wife makes $495,000, and the husband makes $5,000, the husband can presumably contribute to an IRA if they file separately. If the couple remains married, both will benefit from the IRA's tax advantages at retirement.

At first glance the law seems to punish couples who file separately. But at second glance it seems to reward couples who file separately when only one of them earns significant wages - which is often the case with the super wealthy. But that couldn't be right. Congress would never specifically cater to the super wealthy. Of course not. Ever.