Methodology
Calculation Methodology
How Samvat calculates Panchang values, festival dates, tithi, nakshatra, muhurat, and city-sensitive Hindu calendar data.
Core Inputs
Samvat calculations use the date, latitude, longitude, and timezone for the selected city. Sunrise, sunset, solar noon, and moonrise are location-sensitive and can change which civil date carries a Panchang condition.
Tithi is calculated from Moon-Sun angular separation. Nakshatra is calculated from the Moon position along the ecliptic. Sankranti is calculated from the Sun entering a sidereal rashi.
Daily Panchang Flow
For a selected date and city, Samvat calculates local sunrise and sunset, then derives the Panchang limbs for the relevant moments of the day.
The workflow is intentionally explicit: date and place first, astronomical positions second, Panchang limbs third, and observance rules last.
Festival Rules
Annual festival rules specify a calculation type: tithi, sankranti, nakshatra, tithi-nakshatra, fixed Gregorian, or relative. Some festivals use a rule-specific moment such as sunrise, madhyahna, pradosha, or nishita.
The public festival list currently uses an India-baseline Panchang. Personal observance may shift by city when the relevant tithi crosses sunrise, sunset, or midnight.
How to Interpret Differences
When two calendars disagree, compare the city, timezone, ayanamsa assumptions, lunar month system, and the rule moment being used.
A disagreement is not always an error. It can be the result of applying a different regional tradition or testing the tithi at a different moment.
Transparency
Festival pages show the Hindu date and explanation rule so families can see the reasoning, not just the final Gregorian date.
Future updates should continue adding regional variants where a single India-baseline date is not enough.