Managing retainers
If you want to make sure you start each month with a $0 balance on retainer projects/matters, you have a few different options. If you use TimeCache's built-in invoice function, TimeCache can automatically hide the retainer fee entry and all the retainer charge entries from each Job Sheet as you invoice them (with the proper Preferences settings for Invoice options). This allows you to use the same project month after month, adding a retainer amount each month.

Another option is to mark "old" retainer entries on their respective Job Sheets and check the Hide marked entries checkbox at the top of the Job Sheet panel.

Or you can create a "billed items" project for each project you're tracking and move entries to it after the month is up. As an alternative, you could archive projects each month, removing them from the active data file, and creating new project listings (i.e. new Job Sheets) for any continuing retainer jobs.