How do I value the cost of my house that was gifted to me?

[jenny3]

I have a small business and have a  home office in my house.

[MargaretL]

Since the home was the gift to you, the value of the house is the cost (from your mom) OR the Fair Market Value at the time it was given to you- whichever is lower.  You must somehow find the cost from your or your mom's records. As to the FMV, you may ask a real estate agent for market analysis, if you don't have a formal appraisal.