UTC to IST

Enter a time in Coordinated Universal Time and read it in India Standard Time. IST is usually 5 hours 30 minutes ahead of UTC.

Whether the gap holds all year

The gap holds at 5 hours 30 minutes ahead all year, because Coordinated Universal Time and India Standard Time either change their clocks together or not at all — which makes this one of the few conversions you can safely memorise.

Which zones these letters mean

IST here means India Standard Time. It can also mean Irish Standard Time and Israel Standard Time. India is the usual intent and the only one of the three offset by a half hour.

Questions

What does CST actually mean?

It depends who wrote it, and that is the problem. CST is US Central Time and it is also China Standard Time — fourteen hours apart. IST is India, Ireland and Israel. Every conversion page here names the zone it resolved an abbreviation to, rather than quietly picking one.

Why does the difference between two time zones change during the year?

Because countries change their clocks on different dates. The United States moves in March and November, the European Union in the last weekends of March and October, and the southern hemisphere moves the opposite way entirely. For a few weeks each year the usual gap is an hour out, which is when most mis-scheduled calls happen.