Why is Diwali on a different date every year?

The Kartika new moon fell at 17:55 IST on 21 October 2025, and the next one fell at 12:32 IST on 9 November 2026. That's 384 days, which is 13 lunar months rather than 12. The extra month was Adhik Jyeshtha, added earlier in 2026.

Without it, Diwali would have followed the new moon about 354 days later, near 10 October 2026: 11 days earlier, the usual shift. With it, the date moved 19 days later. Over the years the date goes back and forth like this, always staying near the same part of the season, between mid-October and mid-November.

Here's the part that confuses people. The new moon instant in 2026 is on 9 November, but in Delhi, Diwali is on 8 November. The rule asks for Amavasya, the last lunar day of the dark fortnight, to be in force during Pradosh, the evening window after sunset. On the 9th Amavasya ends at 12:32, long before evening. On the evening of the 8th, it's in force, even though the 8th began with a different tithi at sunrise.

In 2025 this got very close. Amavasya ended only about ten minutes after sunset in Delhi on 21 October, so the 20th was chosen there, but it wasn't a clear-cut case everywhere. Your friends in other cities, or abroad in other time zones, can honestly end up on a different night.

Both of these steps are arithmetic, but choosing how to use them isn't. Published panchangs differ slightly on how to measure Pradosh and on what to do when Amavasya overlaps two evenings. In those years a local temple committee or a family priest makes the call. So when you see two dates in the news, it usually isn't that someone got the astronomy wrong. They're applying a rule to a close case.