India Standard Time

Frequently asked questions

Common questions about IST, daylight saving, and how to handle it in software. Can't find what you need? Email [email protected].

Why doesn’t IST observe daylight saving time?

India and Sri Lanka have chosen to maintain a consistent time year-round for simplicity in governance, transportation, and daily life—especially near the equator, where daylight hours vary little across seasons.

What is unique about India Standard Time’s half-hour offset?

IST is one of only a few global timezones with a 30-minute offset (UTC+05:30), historically chosen to balance solar noon between India’s eastern and western cities after independence.

Is IST used only in India?

No—Sri Lanka also uses IST under the Asia/Colombo zone, sharing the exact same UTC+05:30 offset since 2006.

When did Sri Lanka switch to IST permanently?

Sri Lanka adopted UTC+05:30 permanently on April 15, 2006, aligning fully with India’s time zone after experimenting with several offsets.

How does IST affect business across South Asia?

With over 1.5 billion people operating on the same time without DST changes, scheduling across India, Sri Lanka, and neighbor regions is straightforward and reliable.

Does IST ever change in the future?

There are no known plans for India or Sri Lanka to adopt daylight saving or change their current offset.

What’s the history behind India’s time zone?

IST was established during British rule and retained post-independence, chosen to unify the subcontinent under a single standard time despite spanning nearly 30 degrees of longitude.

Are there other half-hour time zones like IST?

Yes—Nepal uses UTC+05:45, and Iran uses UTC+03:30, but IST remains the most widely used half-hour offset by population.

Why does IST have two member zones in timezone.io’s data?

Both Asia/Kolkata (India) and Asia/Colombo (Sri Lanka) observe the same UTC+05:30 offset and neither observes DST, so they are grouped under IST.