Purnima (full moon) and Amavasya (new moon) fasting and ritual days are observed by many families in the US and UK, but an India-computed calendar of 2026 dates is only a starting point for checking your own local date.

Why the India date does not always transfer directly

Tithi boundaries occur at a fixed instant worldwide, but the local calendar date that instant falls on depends on your time zone. A tithi that begins late at night IST can fall on the previous day by US or UK clocks, or the observance can shift by a full day depending on which local sunrise the tithi is measured against.

A practical approach

Rather than assuming your local date matches India’s calendar exactly, check the specific tithi for your own city on the date India lists, and the day immediately before and after, since the correct local date is whichever one the tithi actually prevails on for your location.

A worked example

Take Purnima in July 2026. India’s panchang lists it as falling on July 29, with the tithi starting around 11:48 PM IST on July 28 and ending around 9:15 PM IST on July 29.

Convert that start time to US Eastern (IST is 9.5 hours ahead): 11:48 PM IST on July 28 lands at 2:18 PM EDT, still on July 28. So for someone in New York, the tithi is already running for most of daylight hours on July 28, not July 29. Fasting on the India-listed date of July 29 would mean fasting on the day the tithi has mostly already ended locally.

For London (BST, 4.5 hours behind IST), the same start time converts to 6:18 PM on July 28. Different offset, same conclusion: the working day for the tithi is July 28 locally. This is why we say “check the day before and after” rather than trust the India date directly. It’s a genuine date shift, not a rounding error, and it depends on your specific offset from IST and where the tithi boundary falls that month.

Why sunrise is the anchor, not midnight

Most tithi-based observances are tied to which tithi prevails at sunrise, not which one is active at midnight. A tithi can begin at 11 PM and end at 9 PM the next day, so it spans two sunrises in some calendars and only one in others, depending on your longitude.

Practically: if the Purnima tithi is already active at your local sunrise, that’s your fasting day, even if it began the evening before and ends before your local midnight. This sunrise rule is also why fasting dates for the same tithi can differ between two Indian cities in different time zones from London or New York, not just between India and the West.

Fasting logistics that don’t show up on a calendar

A few things worth knowing if you’re new to keeping these fasts outside India:

  • The fast window follows the local tithi, not the clock. If your local tithi runs from 6 AM to 4 PM, that’s your fasting window that day, not midnight to midnight.
  • Plan the meal the night before. Most people breaking a fast plan the satvik meal (no onion, no garlic, grain-light thali) the evening prior, since a grocery run on a weekday morning in the US or UK is harder to fit in than in India.
  • Temple timing rarely matches the tithi exactly. A temple in New Jersey or Leicester often schedules its Purnima puja for the nearest weekend rather than the exact tithi window, since footfall matters more than precision for a community event. Personal fasting and temple attendance are two separate calendars once you’re outside India.

Confirm your local date

Use the panchang page with your US or UK city selected to confirm which date carries the Purnima or Amavasya tithi where you are.