You can both claim the mortgage interest and the taxes. If this is shared equally, you will divide the interest and taxes by two and you both can include it on your individual returns. Example; If you paid $7,400 in mortgage interest and $2,000 in real estate taxes, you will put on your return $3,700 in mortgage interest and $1,000 in taxes while your girlfriend will put $3,700 in mortgage interest and $1,000 in taxes on hers. You must make sure to input the lenders number and all the information from the 1098 on each return. For more information see IRS Publication 936, page 9. An excerpt is shown below;
IRS Publication 936:
"If you and at least one other person (other than your spouse if you file a joint return) were liable for and paid interest on a mortgage that was for your home, and the other person received a Form 1098 showing the interest that was paid during the year, attach a statement to your return explaining this. Show how much of the interest each of you paid, and give the name and address of the person who received the form. Deduct your share of the interest on Schedule A (Form 1040), line 11, and print “See attached” next to the line. Also, deduct your share of any qualified mortgage insurance premiums on Schedule A (Form1040), line 13. Similarly, if you are the payer of record on a mortgage on which there are other borrowers entitled to a deduction for the interest shown on the Form 1098 you received, deduct only your share of the interest on Schedule A (Form 1040), line 10. Let each of the other borrowers know what his or her share is."
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