@TomD8 wrote:
Alternate solution: set up a joint checking account with your co-owner. Each owner contributes equally to the joint account. Pay all expenses out of the joint account. Then you can divide up the tax deductions any way you want.
I don't see how this removes my objection at all. How can taxpayer 1 claim all the interest as "his share" if he or she only contributed half the money to fund the account that made the payment?
This is what the IRS says,
More than one borrower.
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 paper 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 or 1040-SR), line 8b, and print "See attached" next to the line. Also, deduct your share of any qualified mortgage insurance premiums on Schedule A (Form 1040 or 1040-SR), line 8d.
Similarly, if you're 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 or 1040-SR), line 8a. Let each of the other borrowers know what his or her share is.
Unhelpfully, it doesn't say how to determine each persons' "share".
Here are some articles that support my argument.
https://finance.zacks.com/split-mortgage-interest-tax-deductions-9117.html
https://homeguides.sfgate.com/claiming-tax-deductions-house-multiple-names-deed-67165.html
https://law.scu.edu/same-sex-tax/shared-home-ownership-who-gets-to-take-interest-and-property-tax-de...
