Since the first payment happens in the missionary's first month (whether he starts on the 1st or the last day of the month) that means that no payment is necessary in the month that missionary returns. If you count every month from July 2011 through July 2013 (including July 2013, that is) then you'd have 25 months. We assume that a missionary who left early in the month of July 2011 would return early in the month of July 2013. So only 24 payments would be necessary.
You might want to do an income/expense report with details for that missionary. For the date range, select "All." Just count the number of times $400 was taken out and assume that it should be 24 by the end (if it's an Elder and the timing of going and returning is normal). But according to
https://www.lds.org/callings/melchizede ... s?lang=eng, (You'll have to sign in to see it) any extension of 15 days or more will result in an additional charge. Scroll down to "Extensions."
My real name is Greg Anderson.