01 02 03 04 05 06 07 08 09 10 11 12
31 30 31 30 31 30 30 31 30 31 30 30 -- common year
31 30 31 30 31 30 30 31 30 31 30 31 -- leap year
- All months 30 or 31.- Leap month alternates between 30 and 31.
- Never have more than two consecutive months with the same day.
- Only time two consecutive months have the same number of days are Jun/Jul (30) and (Jan/Dec (31) or Nov/Dec (30)).
- Puts leap month at the end to avoid offsetting only part of the year.
- Any given 3-month span consists of either 91 or 92 days.
- Any given 6-month span consists of either 182 or 183 days, except for spans involving leap month and January, which have 184.
- First half (Jan-Jun) always consists of 183. Second half consists of 183 (leap) or 182 (common).