१The five limbs (pancha-anga)
- Tithi — the lunar day: each 12° the Moon gains on the Sun. 15 in the bright half (Sud, ending at Punam) and 15 in the dark half (Vad, ending at Amas).
- Vaar — the weekday, counted from sunrise to sunrise.
- Nakshatra — the Moon's lunar mansion (27 in all).
- Yoga — from the combined longitude of the Sun and Moon (27).
- Karana — half a tithi (11 kinds; Vishti is also called Bhadra).
२Which tithi is "today"?
The tithi that is running at local sunrise names the day (udaya tithi). Because tithis are 19–26 hours long, sometimes:
- Kshaya tithi — a tithi starts after one sunrise and ends before the next, so no day carries its name.
- Vruddhi tithi — a tithi covers two sunrises, so two days carry the same name.
Some festivals are fixed by the tithi at a different time of day — Diwali by the evening (pradosh), Maha Shivratri by midnight, Ram Navami by midday. Our calendar applies these rules.
३Gujarati months and years
Gujarati months are amant — they run from one Amas to the next. The year starts the day after Diwali (Kartak Sud Ekam, Bestu Varas) and the era is Vikram Samvat. About every three years an extra Adhik maas is added (a lunar month with no solar sankranti) to keep festivals in their seasons.
North Indian calendars are purnimant (month ends at Punam), so their Vad paksha carries the next month's name. That is why Janmashtami is “Shravan Vad 8” in Gujarat but “Bhadrapada Krishna 8” in the North — the same day.
४Jain calendar
- Vir Nirvan Samvat counts from Bhagwan Mahavir's nirvan and begins the day after Diwali (VNS = VS + 470).
- Parvi tithis — Sud and Vad 2, 5, 8, 11, 14, plus Punam and Amas — are days of special observance.
- Pachchakkhan times: Navkarsi = 48 minutes after sunrise. A prahar is a quarter of the daytime: Porsi = 1 prahar after sunrise, Sadh Porsi = 1½, Purimaddh = 2, Avaddh = 3. Chauvihar is completed before sunset.
- Gachchhs and sanghs may follow their own panchang for parvi tithis and Samvatsari — always confirm with your sangh.
५Choghadiya and Rahu kaal
Day (sunrise→sunset) and night (sunset→sunrise) are each divided into 8 choghadiya. Amrut, Shubh, Labh are auspicious and Char is good for travel; Udveg, Rog, Kaal are avoided for new beginnings. Rahu kaal is one-eighth of the daytime, at a fixed position for each weekday, traditionally avoided for starting new work.
६How we calculate
Positions of the Sun and Moon are computed with the Swiss Ephemeris; sidereal positions use the Lahiri (Chitrapaksha) ayanamsa, the standard for Indian panchangs. Sunrise and sunset use the upper limb of the Sun with standard refraction, for the selected city. Times are rounded to the minute; within a minute or two of a tithi change, panchangs can differ.