The Multi API allows you to combine any of the core API's into a single call. This method of calling API for multiple transformations gives you significantly higher performance benfits.
API Credits will be used based on the API Task Credit rules for each API. If Unspecified in the API Documentation this is 1. In the example below, the Task Credits used will be Filter List (1 Credit)
Loop Through Output List (2 Items) and perform 2 functions (4 Credits)
Total = 5 Credits
You then want to use the output from the date to set a followup date as begining of the next month.