Can I Deduct My Mother-in-Law if I'm the Primary Caregiver?

If your father-in-law is still living, and if your mother-in-law files a joint married tax return with him, this disqualifies her as your dependent, and you can’t claim her. Your own filing status doesn't matter, however -- just as long as no one else can claim you as a dependent. For example, you and your spouse do not have to file a joint married return for you to claim an exemption for your mother-in-law.

The IRS does not require that your mother-in-law live with you to qualify as your dependent. For example, it doesn't matter whether you paid for your mother-in-law's care while she was living in your home, or if you paid for her care while she lived elsewhere.

Your mother-in-law cannot have received more taxable income than the amount of the personal exemption you're claiming for her, which is $3,800 for the 2012 tax year. If she received more than this, she's not a dependent. Social Security income usually doesn't count, because in most cases, it is tax-exempt. Even a modest amount of investment or retirement income, however, might put her over the limit.

Your mother-in-law must have depended on you to pay for more than half her living expenses and care during the tax year. For example, if she had $3,000 in income and $12,000 in Social Security benefits, and if her living expenses for the year were $20,000, you wouldn't be able to claim her as your dependent, because she contributed 75 percent of her own support.

If your mother-in-law lived with you, the IRS bases her living costs on the fair rental value of your home, or what you could reasonably charge someone for living there. Your mother-in-law's portion of things like utilities and groceries count as well, and are calculated as a percentage of these costs based on the number of people in your household. For example, if only you, your spouse and your mother-in-law live in your home, her portion of these expenses is one-third.