I have a S corp that I am doing back taxes for. I haven't paid my 2010 California minimum tax of $800. I need to calculate the tax penalty. How would I calculate the tax penalty from when it was due in 2010 to now, May 2013?

As far as the State of California is concerned, although the S corp is technically suspended, the $800 minimum franchise fee due every year continues to accrue. This will happen until the date you actually dissolve the biz and to process this paperwork you will have to get current on the back fees. that fails to pay the $800 annual tax by the original due date is assessed a penalty of 5% of the unpaid tax, plus 0.5% for each month or part of a month (not to exceed 40 months) the tax remains unpaid. This penalty cannot exceed 25% of the unpaid tax. Interest will be due and payable on the late payment. Furthermore, "Interest is due and payable on any tax due if not paid by the original due date. Interest is also due on some penalties. The automatic extension of time to file does not stop interest from accruing. California follows federal rules for the calculation of interest."
I guess you need to contact the ca ftb for more info indetail