I forgot to pay $800 fee for my California S Corp, by April 18.
How much, exactly, do I pay if my payment by Monday.

If you did not pay your minimum tax on time, you will have a late payment penalty and interest.Yor tax software will calculate your franhcise taxes, penalties, and tell you when they are due

the $800 CA minimum franchise tax due by April 18, 2017. The franchise tax is equal to the larger of your CA income multiplied by the appropriate tax rate or the $800 tax. Newly filed CA corps only pay the $150 filing fee the year they incorporate. Whether they owe a franchise fee due next April depends on whether they have been profitable or not their first year. CA requires S corps to pay a 1.5% franchise tax on income, with a minimum tax of $800.so say, your S corp had net income of $100K. The corp will owe state franchise tax in the amount of $1.5K(1.5% of $100K). The minimum CA franchise tax ($800) is due the first quarter of each accounting period and must be paid whether the corp is active, inactive, operates at a loss, or files a return for a short period of less than 12 months.