You have the option to set KC to give every X day free for boarding stays.
Click on File, System Options, Boarding tab.
Enter your option and hit OK when done.

For our option, we are giving every 14th day free. This will apply to boarding stays 14 days or longer.
Gus has an appointment from 9/1 to 9/16, a stay of 16 days. When you create the invoice, he will be charged for 15 days because the 14th day is free.

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