If you are going to itemize your deductions then both of you must itemize even if the other does not have any itemized deductions.
The mortgage interest can be entered by both of you, split how you want, but not more than 100% of the total interest paid between the two tax returns.
See this TurboTax support FAQ for filing jointly or separately when married - https://ttlc.intuit.com/community/married/help/is-it-better-for-a-married-couple-to-file-jointly-or-...
And may I ask why you are filing separate returns? Sometimes people don't realize the differences between filing Joint and MFS.
Unless you have a specific reason to file separate returns,
It is usually better to file Joint. Joint has the lowest tax rates and the highest Standard Deduction. And if you are in a Community Property state MFS gets tricky to figure out. Here's some things to consider about filing separately……
In the first place you each have to file a separate return, so that's two returns. And if you are using the Online version that means using 2 accounts and paying the fees twice.
Many people think they come out better when filing Married Filing Separate but they are probably doing it wrong. If one person itemizes deductions then the other one must itemize too, even if it's less than the standard deduction, even if it is ZERO!
And there are several credits you can't take when filing separately, like the
EITC Earned Income Tax Credit
Child Care Credit
Educational Deductions and Credits
And contributions to IRA and ROTH IRA are limited when you file MFS.
Also if you file Married Filing Separately up to 85`% of your Social Security becomes taxable right away even with zero other income.
How do I file for home interest if my wife and I filed Married, but Separately?
The two of you together can not claim more than 100% of the property taxes or mortgage interest actually paid in the tax year.
If you were "in fact" married on or before Dec 31 of the tax year, and you still want to file separate returns (which makes absolutely no sense economically for taxes), then there's only two requirements that have to be met in order for each of you to claim a percentage of the aforementioned expenses, or for one of you to claim 100% of those expenses.
1) You must be legally obligated to pay it.
2) you must have actually paid it, and be able to prove it if audited on it.
If both names are on the property deed and both names are on the mortgage, then both of you meet requirement #1 above.