How do you find how many months and days from June 15 2009 to March 7 2010?

Months are not a fixed number of days, but March 7, 2010 was 8 months and 20 days after June 15, 2009.

The calculation uses "full months" of various lengths, ending with the 8th full month on February 15, 2010. From there, you have 13 days more in February and 7 in March.

The actual number of days not including the starting day is 264 days.