Can a year have 364 days?

Question

Here's a bit of fun.

If we peek at the dotnet source code, the following comment can be found at the head of the file TimeSpan.cs:

...while a year can contain 365 or 364 days

Should I be worried?

Answer 1

I don't know what the source code comment refers to, but there are some more exotic calendars where a year only has 364 days, e.g. a leap week calendar:

A leap week calendar is a calendar system with a whole number of weeks every year, and with every year starting on the same weekday. Most leap week calendars are proposed reforms to the civil calendar, but some - such as the ISO week number calendar - are simply conveniences for specific purposes.

The ISO calendar in question is a variation of the Gregorian calendar that is used (mainly) in government and business for fiscal years, as well as in timekeeping. In this system a year (ISO year) has 52 or 53 full weeks (364 or 371 days).

One advantage is the better divisibility. A year with 364 days can be divided into 13 equal months. Other calendars using such a system are according to Wikipedia:

• International Fixed Calendar
• Pax Calendar