Tenmonth

Tenmonth is a proposed calendar concept that reorganizes the year into ten months of 36 days each, totaling 360 days. The remaining five days are treated as annual days outside the months to bring the annual total to 365 days in common years, with six such days in leap years.

Each month would consist of 36 days, which could be arranged as four 9-day weeks or six 6-day weeks, depending on convention. Names for the months vary by proposal but are often derived from numbers or seasonal attributions.

Intercalary days are placed at year end as a fixed block or distributed across the year in small segments depending on the model. The leap-year rule adds one intercalary day on leap years to keep the calendar synchronized with the solar year.

History and usage: The ten-month concept has appeared in calendar reform literature as a thought experiment to simplify arithmetic and standardize scheduling; it has not been adopted by any major civil calendar. It is also used in speculative fiction and educational contexts to illustrate alternative timekeeping schemes.

Advantages and drawbacks: Proponents cite arithmetic uniformity and easier cross-cultural date calculations; critics point to disruption of seasonal markers, religious holidays, and software compatibility. Variants of the ten-month idea exist, but no single implementation has achieved widespread adoption.