UK school holiday pricing follows a predictable pattern most travel sites are built around. Eid and Diwali don't follow the same calendar logic. They shift each year against the Islamic and Hindu lunar calendars, creating demand spikes that aren't tied to half-term dates. If your travel is tied to a festival, treat the festival date as your primary planning anchor, then check the UK school holiday overlap separately.
The years to watch are the ones where the two calendars collide. When Eid or Diwali falls inside a UK school holiday window, both demand spikes hit the same dates at once and fares are the steepest of the year, so book earlier than either pattern alone would suggest. In years where the festival sits in normal term time, families tied to school dates and families tied to the festival are competing for different weeks, and pricing is noticeably kinder.
Don't forget the return leg follows its own festival logic. Outbound demand peaks in the days before the festival, and return demand peaks in the days immediately after it, when everyone who travelled out wants to come home in the same narrow window. If your dates have any flexibility at all, shifting the return even a few days past the post-festival rush is one of the more reliable ways to bring the total fare down.