Thirteen months. Twenty-eight days each. One extra day of year. A perfectly symmetrical reckoning of time — now in your pocket.
The fixed 13-month calendar is an alternative timekeeping system in which every month has exactly 28 days (four full weeks), giving the year 364 days across 13 months, plus one extra "Year Day" at the end (two during a leap year). Every date falls on the same day of the week, every year, forever.
No more wondering what day the 15th is. No more months with 28, 29, 30, or 31 days depending on the moon's mood. The calendar becomes a predictable, symmetrical instrument instead of a patchwork of historical accidents.
I didn't invent this — it's a concept proposed by various thinkers over the centuries — but I believe it deserves far wider adoption. I built this app as a practical demonstration: live alongside the Gregorian calendar, cross-reference dates, and feel the difference.
Explore the full calendar in your browser — no install required.
Sideload the Android app directly to your device.
No data collected. No servers. See the full policy.
Time shapes how we think. A chaotic calendar produces chaotic planning. When every month is the same length, budgets, schedules, and rhythms all become easier to reason about. Teams, businesses, and individuals naturally fall into predictable quarterly and monthly cadences instead of constantly compensating for February's missing days or October's arbitrary length.
The app lets you live in both worlds simultaneously — viewing your events through the lens of the thirteen-month structure while staying anchored to Gregorian dates everyone else uses. Think of it as a second sight for time.