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.
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.
This information is descriptive.