Your festival is on your town's day, not India's.

Three facts that explain it

1. The tithi is one instant for the whole world. It changes when the Moon gains another twelve degrees on the Sun. At that moment it is evening in Delhi and morning in New Jersey.

2. A day is kept by the tithi at its own moment. Karwa Chauth is the Kartik Krishna Chaturthi that holds at moonrise. In 2026 that is the evening of 28 October in America, because the Chaturthi has begun by moonrise there, and the evening of 29 October in India and Britain.

3. The clocks move, and not together. Britain's clocks go back on 25 October 2026 and America's and Canada's on 1 November. India's never move. A page that adds a fixed number of hours to India's time is an hour wrong once either country changes, and Diwali on 8 November falls after both.

Kalava does not copy India's times. It computes every sunrise, moonrise and tithi for the town itself, in that town's own time zone with its own clock changes, and checks the result against the published almanacs. How