28 Day 13 Month Calendar. The calendar we use is archaic, cumbersome and a inefficient. It is a perennial calendar as every date is fixed to the same weekday every year.

Under the international fixed calendar plan, each year would have exactly 52 weeks split evenly into 13 months of four weeks and 28 days. The gregorian calendar we’re familiar with was nearly replaced in the 1920s and 30s with the international fixed calendar, with 13.