Originally Posted by Lenny2

You have to pay withholding tax if you pay yourself a salary. That has to be paid every month, it includes estimated withholding plus FICA taxes on your salary.

Estimated tax payments on your bonuses or dividends or any other profits that don't come in the form of a salary don't have to be paid quarterly, but if they're not you have to pay an underpayment penalty at the end of the year.

Personally I don't pay quarterly because the interest rate for underpayment is so low I'd rather use that money as operating capital during the year, and then pay the small interest charge. That's better than being without the money during the year IMO.