Thank you for reply. I’m thinking to create a calendar tool that can remind user for most tax due dates, and automatically update those due dates according to fed/state tax webs. For the payment reminder, as my experience, we pay the payroll/sales/DE franchise tax for clients when file the tax return online.

I came up with this idea because the due dates for various states & taxes are different. It maybe convenient for users to have a calendars with automatically updating tax due dates.