I found out about the International Fixed Calendar in a random conversation with my boyfriend (this is a pretty typical chat for us). I’d not heard of it before, and a quick search on Wikipedia yielded this:
|But then it got me into an interesting spot of bother. During the same conversation, I jokingly told him what my birthday was using this calendar (it uses much of the same language and structure of the Gregorian calendar, but an additional month, Sol, is inserted between June and July), which is a date that looks like 15 days earlier than it really is – both calendars have a year of 365 days, but the months are of different lengths.
I didn’t realise he’d used this date to add to his birthday calendar until my present arrived on 7th July… meaning that I unintentionally had two birthdays this year. Oops.
Compare dates in the Gregorian and International Fixed calendars using this spreadsheet: international fixed calendar