This came straight from Susan Combs, Texas Comptroller of Public Accounts – they are great about communicating with Texas corporations:
The new Online Franchise Tax Calculator (PDF, 263KB) is now available on Window on State Government. This tool allows you to estimate your potential franchise tax liability for report years 2008, 2009 and 2010. Your actual tax liability may differ from the estimate because of special provisions in the legislation.
You may also wish to visit our Franchise Tax Web page for answers to your other franchise tax reporting questions.