@awbaldi wrote:
.....Can I just subtract the tax assessment land value from the cost basis...
Is the assessment broken down into two separate components (land and unit) by actual value (dollar figures) rather than just percentages? If so, you can most likely use the figure provided by the assessor.
If not, you can always try to contact the assessor's office and request an adjustment. Regardless, with the numbers you provided, you will have about a $5,000/year differential over a 27.5-year recovery period so it might not be worthwhile especially considering the accumulated depreciation deductions will be subject to recapture if and when you dispose of the unit.
