The 5-Week Leap Month Calendar has 10 months of exactly 5 weeks, i.e. 35 days, in common years and an additional 11th month of equal length in leap years. Since the year is thus either way too short at 350 days or way too long at 385 days, it’s not really an appropriate solar calendar and the leap month is inserted quite often (43.55%, i.e. almost every other year); the months are also too long to make it a good lunar calendar.