Every year the same thing happens in British Hindu households. Someone’s mum in India says Raksha Bandhan is Friday. The calendar on the kitchen wall — printed in Delhi — agrees. The local mandir says Thursday.

Nobody is wrong. Here’s what’s actually going on.

The short version

A Hindu festival isn’t on a date. It’s on a tithi — a lunar day.

A tithi is the time it takes the moon to move 12° ahead of the sun. It’s an astronomical event: it begins and ends at a precise instant, and that instant is the same moment everywhere on Earth.

But tithis don’t line up with civil days. A tithi can start at 3pm on Tuesday and end at 1pm on Wednesday. So which day is the festival?

The rule is: the day on which that tithi is present at the relevant local moment — usually sunrise, sometimes midnight, sometimes moonrise, depending on the festival.

And “local” is the whole point. London runs 4.5 to 5.5 hours behind India. So a tithi that begins just after sunrise in India begins before sunrise in Britain — and the festival lands a day earlier here.

It’s not a compromise — it’s the correct calculation

This is the part worth understanding: the UK date isn’t a convenient approximation for the diaspora. It’s what the panchang’s own rules produce when you apply them at 52°N instead of 28°N.

Using the Indian date in Britain isn’t more authentic. It’s using someone else’s sunrise.

A traditional almanac open on a desk beside a plain modern wall calendar, with an oil lamp and reading glasses

Two calendars, one answer — and the British reckoning is not a compromise.

Which festivals actually shift

Most don’t. Diwali, Navratri, Maha Shivaratri and Ganesh Chaturthi usually land on the same civil date in both countries.

The ones that regularly move:

Raksha Bandhan — shifted in both 2026 and 2027
Janmashtami — and it can also split between Smarta and Vaishnava observance
Ram Navami — the biggest UK shift of the current cycle (2027)
Ganesh Chaturthi — shifts in 2027
Hanuman Jayanti, Holi, Makar Sankranti — all shifted in recent years

And then there are the timings

Some festivals share the date but not the hour — and here the difference is dramatic:

Karva Chauth ends at moonrise. In 2026 the moon rises over London around 6:31pm; in India, around 8:17pm. Nearly two hours apart. A British family following an Indian timing would break their fast late by a wide margin.
Kali Puja peaks in the nishita (midnight) window, which in London runs roughly 11:15pm–12:15am — again, not the Indian figure.
Navratri muhurats and Holika Dahan windows are all locally computed. In 2026, London’s Holika Dahan window sits near midnight, where India’s was a comfortable evening slot.

Why the month names disagree too

A related confusion. You’ll see Janmashtami described as falling in Shravana by some sources and Bhadrapada by others. Both are right.

North India uses the purnimanta system (months end at the full moon); Gujarat, Maharashtra and the south use amanta (months end at the new moon). Same lunar day — different month label. It isn’t a disagreement about when, only about what it’s called.

The same applies to Maha Shivaratri (Magha or Phalguna) and to when “Sawan” starts — North India begins Shravana about fifteen days earlier than the amanta regions.

What we do about it

We publish UK dates, computed for British local time, and our pandit confirms the observances before each festival. Where a date differs from the Indian one, we say so on our events calendar rather than leaving people to discover it.

If your family calendar disagrees with ours, now you know why — and you’re welcome to ask our pandit. Nobody minds the question; it’s a genuinely good one.

One last thing

If your mum in India says Friday and the mandir says Thursday, you have our sympathy. This page will not win that argument.

But you can point out, accurately, that the mandir is applying the same panchang she is — just at the right latitude.

See our UK dates. The events calendar lists our festivals with British reckoning, confirmed by the mandir’s pandit.