One of the least known benefits of marriage is you can save more for retirement than if you were still single. However, if your wife lost her job, she won't have any income to contribute to her Roth individual retirement plan. You can save the day if you meet the criteria to make a spousal contribution on her behalf.
Usually, if a person doesn't have their own compensation, she can't contribute to a Roth IRA. However, the IRS makes an exception for married couples who file a joint return. The rules say your wife can't put anything into her Roth IRA for the year since she didn't work, not even any savings she might have. However, since she's married to you, the rules say she can share your compensation. That means you can contribute to her Roth IRA on her behalf. This deal isn't available if you file separate returns.
No Double Counting
The contribution limit for a Roth IRA is the smaller of the annual contribution limit or your compensation. Each dollar of compensation can only count once, so your wife's contribution limit is the smaller of the annual contribution limit, or your compensation minus her contribution. This distinction only matters if your compensation is less than double the annual contribution limit. Say the annual limit is $5,000, and you've got $9,000 of compensation. If you put $5,000 into your IRA, you can only contribute $4,000 to your wife's Roth IRA.
Roth IRAs limit who can make contributions each year based on a modified adjusted gross income limit. However, the limit changes annually for inflation. The joint return limit, $183,000 as of 2012, is the same no matter who brings in the income. Simply put, if you made more than the limit, you can't put anything in your wife's Roth IRA because you made too much money.
Combined Contribution Limits
The IRS combines the contribution limit for Roth IRAs with those for traditional IRAs. So, even if you're otherwise eligible, you can't contribute to your wife's Roth IRA if you've already maxed out a contribution to her traditional IRA. For example, in 2012, the contribution limit was $5,000 for anyone under 50. If you've already put that much in her traditional IRA, you can't contribute anything to her Roth IRA.