The Quepennura Leap Week Calendar builds upon the Gregorian Calendar, but has a distinct irregular month layout and an unusual leap cycle.
- Regular months (01, 03–06, 08–11) have 31 days each.
- February (02) and July (07) have only 30 days each.
- December (12) has 25 days in a common year and 32 days in a leap-week year.
Since only the last month of the year has a variable length, all months start on a fixed day of the week (and none of them on Wednesday or Sunday):
- January starts on a Monday to align with international standard ISO 8601.
- February starts on a Thursday.
- March starts on a Saturday to align with alleged Roman or Christian traditions of the Julian calendar.
- April starts on a Tuesday.
- May starts on a Friday.
- June starts on a Monday.
- July starts on a Thursday.
- August starts on a Saturday.
- September starts on a Tuesday.
- October starts on a Friday.
- November starts on a Monday.
- December starts on a Thursday.
For the number of weeks per months, the Thursday rule is explicitly applied, which leads to an irregular pattern:
- January: 4 weeks
- February: 5 weeks
- March: 4 weeks
- April: 5 weeks
- May: 4 weeks
- June: 4 weeks
- July: 5 weeks
- August: 4 weeks
- September: 5 weeks
- October: 4 weeks
- November: 4 weeks
- December: 4/5 weeks
In common years of 364 days, the *weeks* of three consecutive months are counted as a quarter-year, but in leap years of 371 days, the *days* of three consecutive months are counted as a quarter-year. This can be done in one of the following three ways, the first of which is preferred:
- (A) Starting with March: 13:13:13:13 weeks or 93:92:93:93 days.
- (B) Starting with January: 13:13:14:12 weeks or 92:93:92:94 days, so week 5 of September should be week 0 of October in common years and 1 October should be 32 September in leap years.
- (C) Starting with February: 13:13:12:14 weeks or 92:93:94:92 days, so week 1 of February should be counted as week 5 of January in common years and 31 January should be counted as 0 February in leap years.
The leap cycle repeats every 479 years or 24,993 weeks. It has 85 leap weeks in it, spread uniformly. The mean length of a year is therefore 365.24217119 days.