IST is 5 hours 30 minutes ahead of Zulu. Live clocks, the full hour chart and the daylight saving rule that catches people out.
Zulu time is UTC - the clock every flight plan, order and server log is written in, precisely because it never moves. India Standard Time (IST) sits UTC+5:30, which makes it 5 hours 30 minutes ahead of Zulu. In everyday speech the zone is just "India time". Converting one to the other is a single addition, and the only two things that go wrong are the date and daylight saving.
The converter above tracks the current time until you type into it. Enter any Zulu time - 1730Z, 17:30Z or NOW - and it renders the same instant in IST in 24-hour, 12-hour and dated form. The chart below is the same conversion for every hour of the day, so it can be read without typing anything at all.
Every hour from 0000Z to 2300Z. One column is enough - IST keeps the same offset all year. Where the sum crosses midnight the date moves with it, marked in the cell.
| Zulu | ISTUTC+5:30 |
|---|---|
| 0000Z | 05:30 |
| 0100Z | 06:30 |
| 0200Z | 07:30 |
| 0300Z | 08:30 |
| 0400Z | 09:30 |
| 0500Z | 10:30 |
| 0600Z | 11:30 |
| 0700Z | 12:30 |
| 0800Z | 13:30 |
| 0900Z | 14:30 |
| 1000Z | 15:30 |
| 1100Z | 16:30 |
| 1200Z | 17:30 |
| 1300Z | 18:30 |
| 1400Z | 19:30 |
| 1500Z | 20:30 |
| 1600Z | 21:30 |
| 1700Z | 22:30 |
| 1800Z | 23:30 |
| 1900Z | 00:30 +1 day |
| 2000Z | 01:30 +1 day |
| 2100Z | 02:30 +1 day |
| 2200Z | 03:30 +1 day |
| 2300Z | 04:30 +1 day |
The conversions people reach this page for, answered in one line each. IST has one offset all year, so each answer is always right.
Take the four digits, add 5 hours 30 minutes, and roll the date if the result falls outside 00:00-23:59. 1730Z becomes 23:00 IST; 0200Z becomes 07:30 IST.
Controllers and forecasters often drop the minutes and write a bare hour: 16Z means 1600Z, 6Z means 0600Z. Pad it back to four digits and the chart above answers it directly.
Do the arithmetic in Zulu and convert once, at the end, for whoever needs a local time. Adding en-route time to a departure slot in local time and converting afterwards is how the day boundary gets lost. The Zulu time converter does both halves in one box.
Going the other way is the same arithmetic reversed: take the IST time, subtract 5 hours 30 minutes, and write the result as four digits with a Z suffix. 17:30 IST is 1200Z. If the sum crosses midnight the date moves too, exactly as in the chart, just in the other direction.
India has never observed daylight saving, so the offset is +05:30 all year - one column, no seasonal trap. The half hour is the trap instead: 1200Z is 17:30 IST, not 17:00. IST also abbreviates Irish Standard Time and Israel Standard Time; this page is India.
Because neither clock shifts, a conversion written down today is still right in six months. That is unusual - most of the abbreviations on the sibling pages have a second offset for half the year.
All of India on a single zone, plus Sri Lanka on the same offset. Indian airspace files in Zulu like everywhere else, and every Indian outsourcing and on-call handover crosses this half-hour boundary.
Flight plans, METARs, TAFs, NOTAMs and ATC clearances are all in Zulu, and so are military orders, satellite passes and incident timelines. The conversion to IST is the last step, for the people who have to be somewhere at a local hour - a briefing time, a crew report, a maintenance window. Written the aviation way it carries the day of the month too: 141730Z is the 17:30 Zulu of the 14th, which removes the last ambiguity a date shift can create. See military time for the four-digit notation itself.
The same Z closes every ISO 8601 timestamp: a log line stamped 2026-08-20T16:37:05Z happened at 1637Z, and it converts to IST with the same arithmetic as any briefing time.
IST is 5 hours 30 minutes ahead of Zulu (UTC+5:30). To convert, take the Zulu time and add 5 hours 30 minutes: 1200Z is 17:30 IST.
No. IST stays on UTC+5:30 all year, so a single conversion works in every season. Zulu does not change either.
0000Z is 05:30 IST.
Yes, for every practical purpose. Zulu is how UTC is written and spoken in aviation and military use - the Z suffix is the phonetic letter for the zero-offset zone. GMT is the older name for the same clock reading, though the UK itself moves to BST in summer.
Reverse the arithmetic: subtract 5 hours 30 minutes and add the Z suffix. Do the maths in Zulu first and convert once at the end - converting first and adding afterwards is where the date boundary gets lost.
Printed from tcalc.it - free Zulu time converters, hour charts and the daylight saving rules.