The concept of the calender originated from solar year. The earth completes its orbit about the sun in 365 days 5 hr 48 min 46 sec.This is called solar year.
Total Number of months in a year = 12
Total Number of days in a year = 365
Total Number of days in a leap year = 366
If any year is divisible by 4 then the year is called a leap year. For example: 2008, 2012, 2016 etc are the leap years.
To determine the number of days of any mount we count on our hand’s back as shown in second diagram.
Total Number of months of 31 days in a year = 7
Total Number of months of 30 days in a year = 4
Total Number of months of 28 days or of 29 days in a year = 1