Convert IST to CST India Standard Time ↔ Central Standard Time Free Online Secure
Type a time in IST and read it in CST straight away. The offset is −11:30 h, the arithmetic wraps at midnight, and the answer says which day it lands on.
Nothing uploaded
Through the day — Convert IST to CST (India Standard Time ↔ Central Standard Time)
| IST | CST |
|---|---|
| 00:00 | 12:30 |
| 03:00 | 15:30 |
| 06:00 | 18:30 |
| 09:00 | 21:30 |
| 12:00 | 00:30 |
| 15:00 | 03:30 |
| 18:00 | 06:30 |
| 21:00 | 09:30 |
Where these units come from
Until the middle of the nineteenth century every town kept its own noon, set by the sun overhead, and nobody minded that the next town was four minutes behind. Railways ended that: a timetable cannot be written for a hundred local noons. Britain put its railways on Greenwich time in 1847, and in 1884 the International Meridian Conference in Washington chose Greenwich as the prime meridian and sketched the twenty-four-hour scheme we still use. Greenwich Mean Time was the world's reference until 1972, when Coordinated Universal Time replaced it: UTC is kept by atomic clocks and tied back to the turning Earth by leap seconds. The abbreviations on this page name standard time — the winter setting — which is why each one is a fixed number of hours rather than something that drifts through the year.
Where you meet them
A time zone becomes real the moment two people in different places have to agree on one moment: a call between offices, a flight that lands before it took off, a market that opens while you are asleep, a deadline written in somebody else's afternoon. Server logs, train and flight schedules and anything stamped with a time are kept in UTC precisely so that the question can always be settled, no matter whose clock was on the wall.
Questions people ask
What about summer time?
The offsets here are standard-time offsets, the ones a zone keeps in winter. Where summer time is observed, the same places move one hour further on for part of the year and take a different name: Central European Time becomes Central European Summer Time, Eastern Standard Time becomes Eastern Daylight Time. The switching dates are not the same in every country, and the two hemispheres change in opposite months, so for a date inside a summer-time period add an hour to whichever side observes it.
Why isn't every difference a whole number of hours?
Because offsets are decided by governments, not by geometry. India is half an hour off the hour, at UTC+05:30; Nepal is three quarters, at UTC+05:45; the Chatham Islands are at UTC+12:45. Any of these can be changed by law, and several countries have moved their offset within living memory.
Is the answer exact?
Where both units are defined in terms of one another by whole numbers, yes — the page says so above the figure, and the only rounding is in how many digits are shown. Where the ratio has no finite decimal, the page shows twelve significant digits and says the relation is approximate rather than pretending otherwise.
Does anything I type leave my device?
No. The arithmetic runs in your browser; nothing is uploaded and there is no server to upload it to. Load the page once and it keeps working with the network switched off.
The literature festival in Jaipur and the clock in Chicago
A session at the Jaipur literature festival begins at 10:00 IST. A Test cricket match at Eden Gardens opens at 9:30. A concert in the Chennai music season starts in the evening, at 18:00. Anyone living in Chicago, Dallas or Houston who wants to know what the clock says at home at those moments will convert IST to CST. In winter time the calculation is a subtraction: eleven and a half hours. 10:00 IST becomes 22:30 CST on the previous evening, 9:30 IST becomes 22:00 CST on the previous evening, and 18:00 IST becomes 06:30 CST. Any Indian time before 11:30 belongs to the previous day in central America. When America goes onto summer time, between 8 March and 31 October, only ten and a half hours are subtracted.
The page starts with Indian events followed in the middle of America, then gives the rule, the tables and the two zones. The calculation takes place in the browser; no figure reaches a server.
The Jaipur literature festival
Morning sessions
A session at 10:00 IST in January is at 10:30 p.m. CST on the previous evening. Readers in the Midwest follow it live after dinner.
Afternoon sessions
A debate at 16:00 IST is at 4:30 a.m. CST. A “convert IST to CST” calculation made beforehand shows that it falls in the American night.
The Test match at Eden Gardens
The first day
A Test match opens at 9:30 IST, which is 10:00 p.m. CST on the previous evening. Fans in America stay up or watch the repeat.
The lunch interval
The lunch break, at 12:00 IST, is at 12:30 a.m. CST. For a Texan fan it is the middle of the night.
The Chennai music season
Evening concerts
A classical concert in December at 18:00 IST is at 6:30 a.m. CST. Music lovers in Chicago hear it live at breakfast.
Afternoon recitals
A recital at 15:00 IST is at 3:30 a.m. CST. A “convert IST to CST” calculation tells you at once whether it is worth waking up for.
Ganesh Chaturthi in Mumbai
The immersion procession
The processions to immerse the statues begin in the afternoon, around 14:00 IST, which is 3:30 a.m. CDT. The Indian community in Texas watches live at dawn.
The festival evening
The evening prayers, at 19:30 IST, are at 9:00 a.m. CDT. A “convert IST to CST” calculation shows at once that they fall in the American morning.
The Pongal harvest festival
The morning ritual
The boiling of the first rice takes place at sunrise, around 06:30 IST, which is 7:00 p.m. CST on the previous evening. Indian families in Houston watch it after work.
The daytime programme
Games and dances in the square begin at 11:00 IST, which is 11:30 p.m. CST. Whoever does a “convert IST to CST” calculation with the date in view does not mix up the day.
The Goa carnival
The main parade
The parade at the end of winter sets off at 16:00 IST, which is 4:30 a.m. CST. Americans watch live at dawn or in a repeat.
Carnival evening
Evening shows at 20:00 IST are at 8:30 a.m. CST. For a reader in the Midwest it is a morning broadcast.
Sittings of India’s Parliament
Question Hour
Question Hour usually begins at 11:00 IST, which is 11:30 p.m. CST on the previous evening. American journalists based in Chicago follow it live, late in the evening.
Afternoon debates
A debate at 14:00 IST is at 2:30 a.m. CST. A “convert IST to CST” calculation tells you at once whether you can read about it in the morning papers.
How to convert IST to CST, in plain terms
What to do with the minutes
IST is UTC+5:30 and CST is UTC−6. The two clocks are 11 hours 30 minutes apart, with India ahead. From the Indian time on a 24-hour clock subtract 11:30; the half hour is taken off along with the hours.
What to do with the date
A negative result calls for the previous day: add 24. 03:30 IST gives 16:00 CST yesterday, 08:00 IST gives 20:30 CST yesterday, and 10:00 IST gives 22:30 CST yesterday.
Control values
11:30 IST is 00:00 CST. 13:15 IST is 01:45 CST. 16:00 IST is 04:30 CST. 20:30 IST is 09:00 CST. 22:15 IST is 10:45 CST. 23:59 IST is 12:29 CST. With CDT, 20:30 IST is 10:00 CDT, an hour later.
The time zone in the heart of America
Which places it covers
The Midwest, the Gulf coast and all of Mexico run on UTC−6 in winter. With spring the American states move to UTC−5 under the name CDT, while Mexico keeps its clock.
What it means for you
An Indian poster gives Delhi’s local time. Anyone living in Chicago therefore often has to convert IST to CST before making viewing plans.
The clock of a one-zone country
From Gujarat to Assam
All of India uses UTC+5:30, with no move to summer time. Because of the half hour, the minutes of the result change: 19:15 IST becomes 07:45 CST.
The neighbours
Sri Lanka keeps the same time. Nepal is on UTC+5:45, Pakistan on UTC+5, Bangladesh on UTC+6.
Eleven and a half hours on the dial
Working hours
While an office in Delhi works (09:00 to 17:00), it is late evening and night in Chicago (21:30 to 05:30 of the previous day). While Chicago works from 09:00 to 17:00, it is evening and night in India (20:30 to 04:30). The two schedules have no hour in common.
Calls
A call from India at 19:00 IST reaches 7:30 a.m. CST. One from 22:00 IST reaches 10:30 a.m. CST, in the middle of the American morning.
The flight
A plane with one stop that takes off from Delhi at 02:00 IST and flies for nearly twenty hours lands in Chicago at 22:00 IST, which is 10:30 a.m. CST. The ticket shows 02:00 and 10:30, as for a trip of eight and a half hours.
Banking services for Indians in America
Transfers
An Indian counter that accepts transfers until 16:00 IST accepts them until 4:30 a.m. CST. Customers in Texas must send the money the previous evening.
Branch appointments
An appointment for a video call given at 10:30 IST is at 11:00 p.m. CST on the previous evening. A “convert IST to CST” calculation made beforehand shows that the day changes.
The same Indian hour, four moments of the year
Winter
On Thursday 8 January, an event at 09:00 IST takes place at 9:30 p.m. CST on Wednesday 7 January.
The end of February
On Thursday 26 February, 09:00 IST is still 9:30 p.m. CST on Wednesday: America has not yet moved its clock.
Mid-March
On Thursday 12 March, 09:00 IST is 10:30 p.m. CDT on Wednesday, because America moved to summer time on 8 March and India did not.
August and November
On Thursday 20 August, 09:00 IST is 10:30 p.m. CDT on Wednesday. On Thursday 19 November, 09:00 IST is again 9:30 p.m. CST on Wednesday, after America’s return to standard time on 1 November.
Why it is sometimes ten and a half hours
From March to October
From 8 March to 31 October America is on summer time and India is not. The distance between IST and Central time then shrinks by an hour.
How to correct
A “convert IST to CST” calculation made with the winter figure gives, during American summer time, a result an hour too early. The correction is always the same.
Colleagues in Bangalore, colleagues in Dallas
The common hour
A team with members in Bangalore and Dallas meets at 19:30 IST, which is 8:00 a.m. CST. For the Indians it is the end of the day, for the Texans the beginning.
The handover
Work that ends at 04:30 IST reaches Dallas at 5:00 p.m. CST on the previous evening. A written handover keeps the thread.
The world’s clocks, read from Delhi
How many hours to subtract
Relative to Delhi, London is 5 hours 30 minutes behind, Berlin 4:30, New York 10:30, Chicago 11:30, Denver 12:30 and Los Angeles 13:30, all in winter time. Tokyo is 3:30 ahead.
A sample invitation
When it is 20:30 in Delhi, it is 15:00 in London, 10:00 in New York, 9:00 in Chicago and 7:00 in Los Angeles. Whoever puts all the hours in the invitation spares the guests a “convert IST to CST” calculation.
Online lectures from Indian universities
Lecture time
A lecture at 19:00 IST is at 7:30 a.m. CST. Students in the Midwest follow it first thing, before work.
Deadlines
A deadline of 23:59 IST falls at 12:29 p.m. CST the same day. Whoever counts the deadline by home midnight loses whole hours.
India’s weather, followed from Texas
Monsoon warnings
A monsoon-rain warning valid until 18:00 IST expires at 6:30 a.m. CST. Families in Texas following events subtract eleven and a half hours from every hour in the bulletin.
How to read it
Each bulletin carries India’s local time. A “convert IST to CST” calculation for both times shows when the latest version appeared.
When the gap is not the usual one
The 2026 calendar
The gap between IST and CST changes during the year. In 2026: 1 January to 7 March and 1 November to 31 December — CST runs 11 hours 30 minutes behind IST; 8 to 28 March, 29 March to 24 October and 25 to 31 October — CST runs 10 hours 30 minutes behind IST.
What to do about it
During the summer periods the zones are called IST and CDT. The calculator assumes the winter gap of 11 hours 30 minutes; adjust by the difference shown for your date. Whenever you convert IST to CST, check which period the date falls in first.
A day of conversions at a glance
IST into CST
00:00 IST is 12:30 CST (previous day). 01:00 IST is 13:30 CST (previous day). 02:00 IST is 14:30 CST (previous day). 03:00 IST is 15:30 CST (previous day). 04:00 IST is 16:30 CST (previous day). 05:00 IST is 17:30 CST (previous day). 06:00 IST is 18:30 CST (previous day). 07:00 IST is 19:30 CST (previous day). 08:00 IST is 20:30 CST (previous day). 09:00 IST is 21:30 CST (previous day). 10:00 IST is 22:30 CST (previous day). 11:00 IST is 23:30 CST (previous day). 12:00 IST is 00:30 CST. 13:00 IST is 01:30 CST. 14:00 IST is 02:30 CST. 15:00 IST is 03:30 CST. 16:00 IST is 04:30 CST. 17:00 IST is 05:30 CST. 18:00 IST is 06:30 CST. 19:00 IST is 07:30 CST. 20:00 IST is 08:30 CST. 21:00 IST is 09:30 CST. 22:00 IST is 10:30 CST. 23:00 IST is 11:30 CST.
Using the table
Find the IST hour you need and read off the CST hour beside it. The rows come from the arithmetic behind each request to convert IST to CST. Because of the half hour, the minute figure always shifts by thirty; expect :15 to become :45 and :45 to become :15. These rows use the standard (winter) gap; on the dates listed in the period section the gap is different.
Half past every hour
IST :30 against CST
00:30 IST is 13:00 CST (previous day). 01:30 IST is 14:00 CST (previous day). 02:30 IST is 15:00 CST (previous day). 03:30 IST is 16:00 CST (previous day). 04:30 IST is 17:00 CST (previous day). 05:30 IST is 18:00 CST (previous day). 06:30 IST is 19:00 CST (previous day). 07:30 IST is 20:00 CST (previous day). 08:30 IST is 21:00 CST (previous day). 09:30 IST is 22:00 CST (previous day). 10:30 IST is 23:00 CST (previous day). 11:30 IST is 00:00 CST. 12:30 IST is 01:00 CST. 13:30 IST is 02:00 CST. 14:30 IST is 03:00 CST. 15:30 IST is 04:00 CST. 16:30 IST is 05:00 CST. 17:30 IST is 06:00 CST. 18:30 IST is 07:00 CST. 19:30 IST is 08:00 CST. 20:30 IST is 09:00 CST. 21:30 IST is 10:00 CST. 22:30 IST is 11:00 CST. 23:30 IST is 12:00 CST.
A note on the list
Schedules often use :30 slots. Each entry below gives the CST equivalent, so you do not have to convert IST to CST again for them. Read these rows as standard-time values and check the period section for dates where the difference changes.
Not just whole hours
Ten IST readings and the CST result
01:05 IST is 13:35 CST (previous day). 03:20 IST is 15:50 CST (previous day). 05:50 IST is 18:20 CST (previous day). 07:35 IST is 20:05 CST (previous day). 10:10 IST is 22:40 CST (previous day). 13:25 IST is 01:55 CST. 16:40 IST is 05:10 CST. 19:55 IST is 08:25 CST. 22:15 IST is 10:45 CST. 23:05 IST is 11:35 CST.
A word on minutes
A request to convert IST to CST often involves times such as 07:05 or 22:15, so the list below shows ten of them. This pair has a half-hour in its offset, so every :00 becomes :30, every :15 becomes :45 and so on, with the hour carried over. Read these rows as standard-time values and check the period section for dates where the difference changes.
Is it morning or night there?
IST hours and the day in CST
06:00 IST is 18:30 CST (evening). 08:00 IST is 20:30 CST (evening). 10:00 IST is 22:30 CST (night). 12:00 IST is 00:30 CST (night). 14:00 IST is 02:30 CST (night). 16:00 IST is 04:30 CST (night). 18:00 IST is 06:30 CST (early morning). 20:00 IST is 08:30 CST (morning). 22:00 IST is 10:30 CST (morning).
A practical use
The list pairs a IST hour with its CST time and a plain word for the time of day. It tells you at once whether the person you call has had breakfast or gone to bed. These rows use the standard (winter) gap; on the dates listed in the period section the gap is different.
Before you convert IST to CST: a short checklist
Preparation
Check the zone names
IST can also mean Irish Standard Time or Israel Standard Time; here it means India. Beware that CST is also China Standard Time (UTC+8) and Cuba Standard Time (UTC−5); this page uses the North American Central zone.
Use a 24-hour clock
The 24-hour clock avoids a.m. and p.m. slips, so rewrite 4:30 p.m. as 16:30 before anything else. For example, 09:15 IST becomes 21:45 CST (previous day).
After the sum
The operation
Subtract 11 hours 30 minutes. If the result passes midnight, correct the date: readings before 11:30 fall on the previous date.
A second example
An evening check: 22:40 IST gives 11:10 CST.
Common slips when you convert IST to CST
Adding instead of subtracting
Because CST runs behind IST, the result must be an earlier clock reading. A later one points to an addition.
Losing the date
Anything on the IST clock before 11:30 lands on the previous date. Keeping the original date produces a one-day error.
The standard figure in the wrong weeks
On some dates in 2026 the distance between IST and CST differs from the usual one, so read the period list before you apply it.
Confusing the abbreviation
Take care: IST may refer to Ireland or Israel as well, but here it is Indian Standard Time. The abbreviation CST is shared with China (UTC+8) and Cuba (UTC−5); on this page it always means Central North America.
Quick answers
How far apart are IST and CST?
11 hours 30 minutes, and CST is behind IST. That is the standard figure; on some dates in 2026 it differs, as the period list shows.
What do I do to convert IST to CST?
Subtract 11 hours 30 minutes from the IST time, then fix the date if the result passes midnight.
What is 15:30 IST in CST?
04:00 CST in the standard period.
Does the answer change during the year?
Yes, on some dates; the period list above shows which.
Is the time I enter sent anywhere?
No. The calculation runs in your browser.
Other pairs worth a look
See also Convert IST to UTC, Convert IST to EST, Convert WET to CST, Convert UTC to CST, Convert CST to WET, Convert GMT to IST, Convert CET to WET, Convert WET to CET, Convert PST to EST. The opposite direction is Convert CST to IST.
In brief, to convert IST to CST you subtract 11 hours 30 minutes, mind the date change and watch the weeks when the gap differs.