It's included, check it out yourself.

Monthly payment = (P+I). 

Different in Monthly payment = (delta P) + (delta I), where delta P and delta I are opposite, ( if delta P is a positive number, delta I would be a negative number), so when you add them up the values in delta P cancels out the values in delta I. 

I ran the excel just now, still 42 month in breakeven time.