What “perpetual” gets you
- Your birthday is the same weekday — every single year.
- Every quarter is exactly 13 weeks (91 days, four equal seasons).
- Holidays never float. The 10th is always a Tuesday.
- Every month is identical: 28 days, four weeks, starts Sunday.
Not a new idea
- Kodak ran its accounting on it for 61 years (1928–1989).
- Championed by Sandford Fleming, the inventor of standard time.
- The League of Nations judged it the strongest of 130 calendar-reform proposals.
- 120M+ people in Ethiopia & Eritrea live by a 13-month calendar today.
Convert any date
Nothing to switch. SOL runs alongside the calendar you already use — every date maps 1:1 and losslessly, so contracts, taxes, and birthdays never skip a beat.
For business & finance
- 13 equal periods — every P&L covers exactly 28 days of sales and payroll.
- Quarters you can actually compare. Gregorian quarters run 90–92 days; here every quarter is 91.
- Walmart, Target and others already run 4-4-5 fiscal calendars — the workaround that proves the need.
The 13th month
Sol is a new month inserted between June and July — named after the sun and aligned with the summer solstice. That makes 13 months of 28 days: 364 days.
The remaining one or two days a year — Year Day (always) and Leap Day (leap years) — sit outside the weekly cycle, keeping SOL in step with the sun without ever disturbing the weekdays.