Home purchase price plus any capital improvements you made to the house prior to the start date of the home office. By the way, TTColeen misread your question as having started the home office in May. The start date is not clear from your post, but you take a partial amount of depreciation for the years in which you first put in the office in service, and when you took it out of service. Her attachment works for the first year, and you can use the year 40 amounts for the last year. For example, if you took the office out of service in June 2015, you take 1.177% of 4.69% times cost basis for that year of depreciation. Don't worry about the difference between this and AMT depreciation.
