While there are no calendar months that have five full weeks, any month with more than 28 days will always have four weeks and a portion of another. For this reason, months frequently have five of a certain day of the week.
Although no calendar months have five weeks, it can be useful to know which ones have five Fridays, Saturdays or Sundays. To determine this, a person needs to know how many days the month contains and what day of the week it starts on. For a month of 30 days (April, June, September and November), the first two days will occur five times. For months with 31 days (January, March, May, July, August, October and December), the first three weekdays come up five times. February, with only 28 days, usually has four of each day. On leap years, however, the first weekday of February will occur five times.