You can only deduct interest on the first $375,000 of your mortgage if you bought your home after December 15, 2017.

Per IRS Publication 587 Business Use of Your Home, page 18:

Home mortgage interest. You will figure the business portion of your home mortgage interest using Form 8829 (if you file Schedule C (Form 1040)) or the Worksheet To Figure the Deduction for Business Use of Your Home in this publication (if you file Schedule F (Form 1040)). The business portion of your home mortgage interest allowed as a deduction this year will be included in the business use of the home deduction you report on Schedule C (Form 1040), line 30, or Schedule F (Form 1040), line 32. If you cannot deduct the business portion of your home mortgage interest in full this year, you will carry over the remaining home mortgage interest to a subsequent year in which you use actual expenses to figure your business of the home deduction.

If you itemize your deductions on Schedule A (Form 1040), only include the personal part of your deductible mortgage interest on Schedule A (Form 1040), lines 8a or 8b. The personal portion of your home mortgage interest will generally be the amount of deductible home mortgage interest you figured when treating all home mortgage interest as a personal expense and applying the Schedule A (Form 1040) limits on deducting home mortgage interest, reduced by the business or rental portions deducted or carried over as a business or rental expense on Schedule C, E, or F, or any form other than Schedule A. Home mortgage interest that exceeds the amount you figured after applying the Schedule A (Form 1040) limits on deducting home mortgage interest is not deductible as a personal expense.

Real estate taxes. You figure the business portion of your real estate taxes using Form 8829 (if you file Schedule C (Form 1040)) or the Worksheet To Figure the Deduction for Business Use of Your Home in this publication (if you file Schedule F (Form 1040)). The business portion of your real estate taxes allowed as a deduction this year will be included in the business use of the home deduction you report on Schedule C (Form 1040), line 30, or Schedule F (Form 1040), line 32. If you cannot deduct the business portion of your real estate taxes in full this year, you will carry over those real estate taxes to a subsequent year in which you use actual expenses to figure your business of the home deduction.

If you itemize your deductions on Schedule A (Form 1040), only include the personal part of your real estate taxes on Schedule A (Form 1040), line 5b. The personal portion of your real estate taxes will generally be the amount of real estate taxes you paid for the home reduced by the business or rental portions deducted or carried over as a business or rental expense on Schedule C, E, or F, or any form other than Schedule A.

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