Many disagree, despite the widespread belief that a seven-day workweek originated in Babylon and is based on lunar cycles. Some say the Jewish people came up with a similar approach to dividing the month for entirely different reasons. The evidence supporting the latter argument seems to point to the employment of such seven-day cycles by Judaists, independent of the moon, as early as the sixth century BC.

Even though the where, when, and why of the invention of weeks remain a mystery to us one thing is certain: a sizable portion of the globe still employs weeks with seven days. which also marks when the work days (also school days) and when the rest days are. 

By 1955, the US, Canada, and the United Kingdom had adopted the two-day weekend. That was the result of several circumstances, and companies took decades to embrace the concept. Only in the 1970s did the 40-hour work week become the norm in Europe, and then the Middle East as well. This is typically used in conjunction with the Gregorian calendar, albeit not only. The majority of nations also share the custom of having two days off each week; however, cultural differences may affect which days these are. The majority of Western civilizations see Saturday and Sunday as their days off and Monday through Friday as their workdays.

Some nations have one-day weekends or weekends that begin on Friday and conclude on Saturday, in which case this calculator is not appropriate.