A calendar that follows the moon but inserts a month to keep up with the sun.
A lunisolar calendar counts lunar months and periodically inserts a thirteenth to stop the year drifting away from the seasons. The Chinese, Hebrew and most Hindu calendars work this way, as did many others.
The inserted month is what distinguishes the family. A purely lunar calendar like the Hijri drifts through the seasons; a lunisolar one stays roughly in place, so Chinese New Year always falls in winter and Passover always in spring, but neither on a fixed Gregorian date.
The consequence for anyone holding dates is that these festivals move within a window rather than moving steadily. Chinese New Year lands somewhere between late January and late February and cannot be predicted by adding a constant.
Two lunisolar calendars, each keeping its festival in the right season without fixing it to a Gregorian date.
| 🇨🇳 | Saturday 6 February 2027China | Spring FestivalChinese New Year, always in winter and never on a fixed date. |
| 🇮🇱 | Thursday 22 April 2027Israel | Passover — first dayThe Hebrew calendar inserts a month seven times in nineteen years to keep Passover in spring. |
The Hijri calendar is purely lunar and inserts nothing, so it drifts about eleven days a year against the seasons.
Intercalation is the mechanism — the inserted day or month. Lunisolar describes a calendar that uses it to reconcile two cycles.
See also hijri calendar · chinese calendar · hebrew calendar · intercalation
We hold this as rule_type: chinese_lunisolar, hebrew_date, hindu_date. See what we hold.