A perpetual, single-page calendar for the whole year — no flipping between months. Every month is grouped by the weekday it starts on, every date-of-month is grouped by its position in a 7-day cycle, and lining the two up tells you the weekday instantly.
Inspired by Ethan Siegel's one-page calendar concept for Big Think.
- Rows group dates that are always 7 days apart (1, 8, 15, 22, 29 / 2, 9, 16, 23, 30 / etc.), since these always share the same weekday within a given month.
- Columns group months that start on the same weekday.
- Row 1 lines up with each month's actual starting weekday; each row after that shifts one weekday to the right, since moving one row down means moving one day later in the month.
- Leap years insert Feb 29, shifting every month from March onward one weekday later — which is why the month groupings look different from year to year.
- A normal year (365 days = 52 weeks + 1 day) shifts next year's calendar forward by one weekday; a leap year (366 days) shifts it forward by two.
MIT License. Free to use, modify, and distribute.