How Unmarried Co-Owners Split the Mortgage Interest Deduction
Because you aren’t married, you can’t file a joint return. Under IRS Publication 936, each co-owner who is liable on the mortgage can deduct the interest they actually paid. How you split it depends on where the money came from:
- If you each pay from your own account, each of you deducts what came from your own funds.
- If you pay from a joint account, you typically split it by how much each of you put in. Equal contributions mean a 50/50 split.
Either way, keep bank statements that show who paid. They’re your record if you need to back up your share.
What Itemizing Means for Your Mortgage Interest
Itemizing vs. the Standard Deduction
The mortgage interest deduction only helps if you itemize. Itemizing means listing your eligible expenses on Schedule A (Form 1040), the form for itemized deductions. You do this instead of taking the standard deduction, a flat amount you can subtract without listing expenses.
For 2026, the standard deduction is $16,100 for single filers and $24,150 for head of household, based on the IRS’s 2026 inflation adjustments. Like other tax deductions, itemizing pays off only when your itemized total is bigger than your standard deduction.
Why Each Partner Decides Separately
Since you file separate returns, one of you can itemize while the other takes the standard deduction. Unmarried partners aren’t bound by the married-filing-separately rule that requires both spouses to itemize if one does.
How the Split Can Change Your Deduction
That separate choice matters, because splitting the interest can leave you both below the standard deduction. Here’s an example with $18,000 of mortgage interest, assuming each partner files single and has no other itemized deductions.
| Scenario | Partner A’s interest | Partner B’s interest | Result |
|---|---|---|---|
| Split 50/50 | $9,000 | $9,000 | Both take the $16,100 standard deduction |
| Partner A pays it all | $18,000 | $0 | A itemizes $18,000, and B takes the $16,100 standard deduction |
In the second scenario, Partner A’s deduction is $1,900 larger than the standard deduction. Each of you can deduct only interest you actually paid, so your split has to match how the payments really happened.
How Mortgage Debt Limits Apply to Unmarried Partners
Acquisition debt is the mortgage you took out to buy your home. You can generally deduct interest on the first $750,000 of it ($375,000 if married filing separately), or $1 million for debt taken on before Dec. 16, 2017. For unmarried co-owners, the IRS generally applies that limit per taxpayer. This is the position in Action on Decision 2016-02, which follows the Ninth Circuit’s Voss decision. So each of you can deduct interest on up to $750,000 of a newer loan.
What to Do if Form 1098 Lists Only One of You
Form 1098, the Mortgage Interest Statement, is the form your lender sends showing the interest you paid. Lenders issue it once they receive $600 or more in interest, according to the Form 1098 instructions. It often lists only one borrower’s name and Social Security number.
Here’s how to report your share:
- If you’re the borrower named on the 1098, deduct only your share on Schedule A line 8a. Then tell your partner their share.
- If your partner received the 1098, deduct your share on Schedule A line 8b and print “See attached” next to the line.
If you’re in the second group and file a paper return, attach a statement explaining that your partner received the form. Show how much interest each of you paid, plus the name and address of the person who received the Form 1098.
