Welcome‎ > ‎My Stuff‎ > ‎

# The 13 Month Sol Calendar

### Configuration:

• Twelve contiguous and identical months of exactly 28 days.
• The last, thirteenth month of the year (December) has 29 days normally and 30 days in a leap year.
• The new month (Sol) occurs between June and July.

### Features:

• Avoids the use of intercalary days and the disruption of the standard week.
• Implementations of 13 period financial calendars are already in wide use in business and accounting.
• Placing the new month (Sol) at mid-year minimizes the seasonal displacement of the traditional months.
• Placing the extra day(s) year-end allows all months to be identical for their first 28 days in any given year.
• Peculiarities: Any year beginning on a Sunday will feature thirteen Friday the 13ths. Blue moons (a second full moon in a calendar month) will become even more rare since they can only occur in December. More birthdays will be celebrated on the 28th over the next century, but in declining numbers.
• Although not perpetual, the calendar does offer an easy method for date/day calculations:

### Simple Calculations:

To calculate any day or date in a given year you only need three bits of information. First, what day of the week did January 1st fall on? Secondly, is this a leap year? Lastly, remember the numbers 1, 8, 15 and 22 (1, 1+7, 1+14, 1+21).

Let's assume January 1st was a Friday and it's a leap year. That means that the first, eighth, fifteenth and twenty-second day of every month is a Friday. The twenty-ninth day of December (1+28) is also a Friday and, since it's a leap year, Saturday the 30th is the last day of the year. The calculations are simple enough to do in your head:

What is the third Monday in May? - Again assuming January 1st was a Friday, the third Friday in any month is the 15th so, with a bit of addition on our fingers, we discover the third Monday is the 18th.

What day of the week is August 13th? Well August 8th is a Friday (as is August 15th) so with a bit more finger work, either adding or subtracting, we deduce the date is a Wednesday.

### Calendar Examples:

 06 Mo Tu We Th Fr Sa Su 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
 07 Mo Tu We Th Fr Sa Su 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
 08 Mo Tu We Th Fr Sa Su 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30