Panchang and the civil calendar: what differs
A panchang is a traditional almanac built on the tithi, vara, nakshatra, yoga and karana. The civil calendar counts days and months by the Sun and by fixed rules.
What it is
The two differ in their unit of time: the civil day runs midnight to midnight, while the panchang day runs from sunrise. The panchang also tracks the Moon's position in detail.
How it is worked out or read
The panchang needs the sidereal positions of the Sun and Moon at sunrise, and the civil calendar does not. Festival dates often follow the panchang, so the two can disagree by a day.
Where it appears on this site
The panchang tool shows both the civil date and the panchang fields.
Two units of time
The civil day runs from midnight to midnight and is counted by the clock. The panchang day runs from sunrise to sunrise and is defined by the Sun's rising. A date on the calendar and a date in the panchang can therefore cover different stretches of time, and an event just before midnight may belong to one day in the civil calendar and to the previous day in the panchang. Reading a date always means asking which unit it refers to.
Months and years
The civil year is the solar year of 365 or 366 days, and its months are fixed by the calendar rules. The panchang uses the lunar month for its tithis and the solar year for the sankrantis. Festivals fall on tithis, so they move against the civil calendar, while the Sun's entries into the signs fall on solar dates. A complete calendar for a Jyotish user therefore holds both systems, and a reader should expect the lunar festivals to shift from one civil year to the next.
What to do when they disagree
When a civil calendar and a panchang disagree about a festival, the usual cause is the rule that fixes the festival date, not an error in either. Check which tithi and which moment the festival rule uses. The panchang shows the tithi and its end time, which is usually enough to see why the two calendars differ. This site shows both the civil date and the panchang fields, so the reader can make the comparison directly.
Living with both calendars
Many households use both a civil calendar and a panchang, and each serves a different purpose. The civil calendar organises work and travel, while the panchang guides the traditional timing of festivals and rites. Keeping both in view avoids confusion when a festival date and a working day fall in different places.
Why festivals move in the civil year
Festivals set by the lunar calendar move through the civil year, sometimes falling early and sometimes late. A reader who knows this is not surprised when a festival changes its civil date, and can plan around the panchang date instead.
One date, two readings
The same day can be read twice: once as a civil date, once as a tithi.