Why 13-Month Calendars Fail — and the 0.0000022-Day Fix
The real math behind the failures: where day 365 goes, why fixed calendars drift from the seasons, and the 365 + 1/4 − 1/128 leap rule that lands within 0.0000022 days of the tropical year.
Thirteen Months, Written Down.
Essays on the mathematics, history, and quiet philosophy of the 13-month year — written by the people building it.
What Is a 13-Month Calendar? The Complete Guide
Twelve eternal 28-day months plus one correction month: how the structure works, where the month names come from, a 175-year history, and an honest pros-and-cons ledger.
Meet HEXA — the 13th Month You've Never Heard Of
Every 13-month calendar has an extra month. HEXA is the one that keeps every familiar name and season in place — and gives late summer a room of its own.
13-Month Calendar FAQ: Every Question, Answered Honestly
Do weeks still have seven days? What happens to birthdays? Is it more accurate? Fourteen questions, precise answers, trade-offs included.