What Calendar Has 13 Months. The united nations has decided to adopt a new calendar system featuring 13 months, each consisting of 28 days, and an extra day added as a holiday at the end of the year. This program converts gregorian calendar date to international fixed calendar (ifc) date and vice versa.

The new calendar is much easier to. The calendar has 13 months, with a new month, sol, inserted between june and july, representing the summer solstice.