Not one calendar but many — regional lunisolar reckonings that disagree by design.
There is no single Hindu calendar. Several regional systems — Vikram Samvat, Shalivahana Shaka, the Tamil and Malayalam calendars and others — coexist, differing in the era they count from, whether a month begins at the new or full moon, and how the leap month is placed.
The consequence is that one festival can fall on different days in different states of the same country, and that a national holiday list for India is a negotiated artefact rather than an arithmetic one.
Most dates derived this way are recorded as estimates. The astronomy is calculable; which calculation a given authority follows is a matter of regional practice.
The same festival, computed on a Hindu reckoning, observed in two countries a hemisphere apart.
| 🇮🇳 | Tuesday 23 March 2027India | HoliPrecision: estimate — the regional reckonings do not always agree. |
| 🇬🇾 | Tuesday 23 March 2027Guyana | PhagwahThe same festival under its Caribbean name, a public holiday. |
Most Hindu calendars are lunisolar, but so are the Chinese and Hebrew ones. The distinguishing feature here is that several coexist and disagree.
See also lunisolar calendar · intercalation · precision · epoch
We hold this as rule_type: hindu_date. See what we hold.