When does my monthly submission start over?

When does my monthly submission total start over?  Is it based on the first of a calendar month or is it based off of the date I signed up?

I guess you are referring monthly limits. The monthly limits' counters are set to zero at the beginning of every month. You can find further details in our user guide: Understanding Your Account Usage and Limits 

If you are talking about your next billing date, you can check it out on your invoice page. Please let us know if you have any further questions.