Default [Q] Following month and previous month dates

Hi, I am trying to create a Progress Bar to indicate where I am in the billing cycle of my phone plan.

Since my billing cycle starts on the 17th of every month, I want to set the Min Value as the current or previous 17th on the calendar and the coming 16th (of this/next month) as the Max Value of the progress bar. Does anyone know how I would call these dates? I've been reading through this forum and the one at zooper.themerapp.com and am still stumped at this problem.

Thanks in advance