If you want to split those deductions 50-50 then GF will have to amend her tax return after it has been fully processed. You cannot "double dip" and each claim 100%. If you are entering mortgage interest you are both already filing on a Form 1040 with a schedule A for itemized deductions.
One thing for you to consider--itemized deductions do not do you any good unless they exceed your standard deduction. By splitting the mortgage interest and property tax, it is possible that neither of you will benefit from claiming it. Crunch some numbers and see.
STANDARD DEDUCTION
Your itemized deductions have to be more than your standard deduction before you will see a change in your tax owed or tax refund. The deductions you enter do not necessarily count “dollar for dollar;” many of them are subject to meeting tough thresholds—medical expenses, job-related expenses, casualty and theft losses, for example, must meet thresholds that are pretty hard to reach. The software program uses all the IRS rules that apply to the expenses you enter, and it tells you if you have enough to use your itemized deductions or if using the standard deduction is more advantageous for you. Here are the Standard Deductions for 2017
Your standard deduction lowers your taxable income. It is not a refund
2017 Standard Deductions
Single $6350 (65 or older + $1550)
Married Filing Separately $6350 (65 or older + $1250)
Married Filing Jointly $12,700 (65 or older + $1250@)
Head of Household $9350 (65 or older + $1550)
Look on line 40 of your Form 1040 to see your itemized deductions
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
