How we calculate the panchang

Every date and time on Aarti is worked out for the city you choose, in its own time zone, from the positions of the Sun and Moon. Nothing is copied from another calendar.

The day starts at sunrise

The Hindu day runs from one sunrise to the next. The tithi, nakshatra, yoga and karana shown for a day are the ones running at that city's sunrise, with the time each one ends.

The calculation

• Sun and Moon positions come from the open-source astronomy-engine library.
• Sidereal positions use the Lahiri ayanamsa, the standard for Indian panchangs.
• Months follow the North Indian (purnimanta) count, where a month ends on the full moon. In the South Indian (amanta) count the dark half belongs to the month before.
• Rahu kaal, Yamaganda and Gulika are eighths of the daylight; Abhijit is the middle fifteenth of the day; Brahma muhurta is the two fifteenths of the night that end one fifteenth before sunrise.

Festival dates

Each festival is fixed by its lunar day at the moment its puja is done, in your city: dusk (pradosh, sunset through the first fifth of the night) for Dhanteras and Lakshmi Puja, the hour before sunrise for Choti Diwali, sunrise for Govardhan Puja and Chhath, and the afternoon (aparahna, the fourth fifth of the daylight) for Bhai Dooj. Because sunrise and sunset differ by city, a festival can fall on a different day in New York, London, Sydney and India.

We do not yet calculate the narrower Lakshmi Puja muhurat that some panchangs print, which is timed to a fixed rising sign (Vrishabha) inside the evening window.

Checked against Drik Panchang

On October 24, 2026 we compared the Diwali week dates for 11 cities and key times for several of them with Drik Panchang. Every date matched, and the times were within 2 minutes. Your family or temple calendar may still keep a day differently, and local custom takes precedence.

Cities

City coordinates and time zones come from GeoNames, used under the Creative Commons Attribution 4.0 licence.

Corrections

If a date or time looks wrong for your city, write to support@tryaarti.com with the city and date.