If you plan to claim a deduction for your medical expenses, there are some new rules this year that may affect your tax return. Here are eight things you should know about the medical and dental expense deduction: AGI threshold increase. Starting in 2013, the amount of allowable medical expenses you must exceed before you can claim a deduction is 10 percent of your adjusted gross income. The threshold was 7.5 percent of AGI in prior years. Temporary exception for age 65. The AGI threshold is still 7.5 percent of your AGI if you or your spouse is age 65 or older. This exception will apply through Dec. 31, 2016. You must itemize. You can only claim your medical and dental expenses if you itemize deductions on your federal tax return. You can't claim these expenses if you take the standard deduction. Paid in 2013. You can include only the expenses you paid in 2013.