(a) The names of the months (January, February, March, etc.) remain the same every year. (b) The number of days in most months remains the same every year, but February changes — it has 28 days in common years and 29 in leap years. (c) A week always has 7 days - Monday through Sunday. This never changes. (d) The number of Sundays in a month or year can change depending on which day the year or month starts. (e) A year always has 52 weeks (with 1 or 2 extra days). This remains the same every year.