When you're married filing separately, who claims mortgage interest and property taxes?

[Vanessa A]

Whichever one of you paid it can claim it.  If you paid it from a joint account, then you can split it. 

Be aware, that if one of you are taking the itemized deductions (claiming the mortgage interest and property taxes) that both of you must itemize.  This means if one person takes the itemized deduction and the other person has little to no itemized expenses to take, they will likely end up paying more in taxes as their taxable income will not be higher. 

[xmasbaby0]

Why do you want to file that way?  That is usually the worst way to file.  You will have to agree as to who uses the itemized deductions or what percent of them you each use, unless you are in a community property state.

If you were legally married at the end of 2022 your filing choices are married filing jointly or married filing separately.

Married Filing Jointly is usually better, even if one spouse had little or no income. When you file a joint return, you and your spouse will get the married filing jointly standard deduction of $25,900 (+$1400 for each spouse 65 or older)  You are eligible for more credits including education credits, earned income credit, child and dependent care credit, and a larger income limit to receive the child tax credit. 

If you choose to file married filing separately, both spouses have to file the same way—either you both itemize or you both use standard deduction. Your tax rate will be higher than on a joint return. Some of the special rules for filing separately include: you cannot get earned income credit, education credits, adoption credits, or deductions for student loan interest. A higher percent of your Social Security benefits may be taxable. Your limit for SALT (state and local taxes and sales tax) will be only $5000 per spouse. In many cases you will not be able to take the child and dependent care credit. The amount you can contribute to a retirement account will be affected. If you live in a community property state, you will be required to provide additional information regarding your spouse’s income. ( Community property states:  AZ, CA, ID, LA, NV, NM, TX, WA, WI)

 If  you are using online TurboTax to prepare your returns, you will need to prepare two separate returns and pay twice.

https://ttlc.intuit.com/questions/1894449-married-filing-jointly-vs-married-filing-separately

https://ttlc.intuit.com/questions/1901162-married-filing-separately-in-community-property-states

https://ttlc.intuit.com/questions/1894449-is-it-better-for-a-married-couple-to-file-jointly-or-separ...