Susan, Margaret and Janine are both correct. To give you an example I currently have listing priced at about $320,000 that is on the tax rolls for about $85,000. It has not been appraised in years. That is not a typical example but it shows what does happen in Montgomery County. The best way to know what your home is worth is to consult with a licensed real estate agent and get neighborhood Comparative Market Analysis.
Ron

Susan,
Janine is correct, Montgomery county is notoriously know for being low on appraisals, they have raised some this year and will more next year and if you are missed there you are going to be safe for some time.
We have a real problem when someone comes in from an area where the tax appraisals are right on and they want to put in offers based on the tax appraisals here,. Needless to say our sellers are quite insulted.
Margaret

Most likely not. The appraisal district normally looks at what has currently sold in your neighorhood or around you that are likewise properties. They do not take into consideration (because they have no way of knowing) any updates made to the home, additions, etc. Montgomery County is notorious for being "behind" on the evaluations and getting items updated on their tax rolls.