Finding the month number!
We know that January has 31 days. A week has 7days so every date in February will be 3 days later than the same day in January. (28 is 4 weeks exactly. 28+3=31). For instance, if January 1st of any given year falls on Saturday, February 1st of that year will be 3 days later. That is on Tuesday. Following the same pattern for all the months, the following table is calculated.