February is not 0.9 months
The number of days in a month varies and is not always 30 days. This app calculates one month always = 30 days.
The entire month of February 2015 had 28 days. This app says 1 month = 0.9 month. 1 year = 0.99 years.
There is a much easier way to calculate months without using days. 1 year = 12 months and the difference between months = # of months.
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Date Difference Calculator