I had a request for a form to count the number of days between two date pickers as one of it’s functions. All that you need to make this happen is add two date picker controls and one text field to display the count. I have included an InfoPath sample form that explains this in detail and should provide you with the knowledge to add something like this to one of your forms.
I originally found this form on the following site when I faced this issue: https://alecpojidaev.wordpress.com/2008/12/30/infopath-codeless-programming-walkthrough-2/
Alec Pojidaev has many great techniques for using no code solutions which I am a big fan of. I suggest you check out his site to see all of the advanced features he has laid out.
Click the link below to download the zip file.