*Rokuyo* is a six-day cycle sometimes printed on Japanese calendars. The six labels are *taian*, *butsumetsu*, *sensho*, *tomobiki*, *senbu*, and *shakko*. Each is traditionally associated with good or bad fortune, so rokuyo may come up when people choose dates for weddings, funerals, and other important events.
These labels have no legal force or scientific authority. A government procedure does not become invalid because it takes place on *butsumetsu*, and a contract does not become stronger because it is signed on *taian*. Rokuyo is not calculated from astronomy, nor is it an official Buddhist teaching that people are required to follow.
It can look more official than it is because people encounter it in ordinary places, including calendars and wedding venues. Being widely recognized, though, is not the same as having an official basis.
Many Japanese people do not know the meaning of all six days in detail. They may know that *taian* is considered lucky and *butsumetsu* unlucky, while being unable to explain *sensho*, *tomobiki*, *senbu*, or *shakko*. Rokuyo is often less a carefully understood belief system than a vague sense that *taian* is good and *butsumetsu* is bad.
Even so, some families avoid *butsumetsu* when arranging a wedding. This does not necessarily mean they truly believe that marrying on that day will cause misfortune. A person may ignore rokuyo when making plans alone but decide there is no reason to choose a date that parents or relatives dislike.
The custom of avoiding funerals on *tomobiki* is also not a legal requirement or an official Buddhist rule. People may choose another day simply because the custom has existed for a long time and someone in the family is likely to care.
It would be wrong to treat rokuyo as part of Japanese law, science, or formal Buddhist doctrine. It would also be slightly misleading to assume that nobody pays attention to it because it has no official basis. Many people do not necessarily believe in rokuyo. They simply avoid certain days when doing so prevents unnecessary objections or awkwardness.