Difference Between CST and IST

Trying to crack an International business deal, calling an NRI friend or relative, traveling abroad are some of the events when we need to convert IST to CST or vice-versa.


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The calculation for conversion is considered concerning GMT (Greenwich Mean Time) though it’s not practically possible to memorize and study universal time zones, therefore, taking reference to GMT and UTC is always helpful for time-zone results.

Multiple countries have similar acronyms for CST and IST like China, Taiwan, Israel, and many specifically “China Standard Time”, “Chung Yuan Standard Time” made people confuse with acronyms of CST.

China takes into account approximately 5 distinct standard zones whereas Beijing has its separate time zone. Moving further to explore more possible differences between CST and IST.


The difference between CST and IST relates to the time gap, where CST lags before IST by 11:30 hours or IST is forward by 11:30 hours of CST. In detail, they both are known as Indian Standard Time and Central Standard Time whereas CST time is considered in North America and IST for India as the name suggests. CST is having a huge area for observation of time with ample states whereas IST is observed in a few Asian Countries only.


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CST (Central Standard Time) is used in Belize, Guatemala, Honduras, El Salvador, Nicaragua, and Costa Rica in Central America.

Although in major parts of America CT (Central Time) is supposed to be observed by the people of America and Canada.

CST is observed by the US citizens is differ from season to season as they for Daytime Light saving and tend to reset the clock as per season.

IST (Indian Standard Time) also known as IT (Indian Time) is observed through Allahbad (Now Praygraj) in India to set the standard time across India. For referring Indian Time, Pryagraj is 82.5 degrees East from PM (Prime Meridian).

IST was introduced in the year 1955, earlier Bombay and Calcutta times were considered to decide the standard time of the country from 1948 to 1955 after independence.

Comparison Table

Parameters of ComparisonCSTIST
Followed by CST is followed by 9 countries in the world and mainly in the US.IST is followed by 2 countries in Asia namely India and Sri Lanka.
GMT VariationCentral Standard Time is 6 hours deducted from GMT.Indian Standard Time is 5 hours and 30 minutes added to GMT.
Time-GapCST is 11 hours 30 minutes before Indian Standard Time.   IST is 11 hours 30 minutes forward from Central Standard Time.
Observation Period.CST is followed during the summer season in North America and CT is observed during winter.IST is observed throughout the year in India and Sri Lanka.
Effective yearCST came into effect in 1833 as a standard time using 4 time zones.India started using IST from the year 1955.

What is CST?

CST is the term as defined earlier Central Standard Time followed by the people of North America specifically in the summer season. It is derived by subtraction of 6 hours from GMT (Greenwich Mean Time).

Identification of CST is based upon the 90th Meridian west of Greenwich, here we mean the solar time. CST time conversion is major in demand for digital business purposes.

The calculation of CST is done with the help of GMT which refers to Royal observatory and UTC (Universally Coordinated Time) both UTC and GMT are equal when fractions of seconds are not important.

Therefore hours of CST can be derived as UTC-6 which applies to 8 or more countries in the world including Mexico, the Caribbean Islands, Eastern part of the Pacific Ocean.

To cover journeys in different time zones, people of America followed CST before observing CST they were using the position of the sun to calculate exact time.

Initially, CST was observed in four zones namely eastern, mountain, central, and sea specifically for America’s rail tracks.

Since only Northern and central territories are following timeclock of CST apart from this eastern states of America are observing EST which is one hour forward from CST. As in CST, it’s 9:00 AM then there will be 10:00 AM in EST.

A similar gap is huge in the case of comparison between CST and IST.

What is IST?

Indian Standard Time is considered with the difference of 5 hours and 30 minutes from Greenwich Mean Time (GMT).

The Indian time calculation standards are introduced in mid-1955 where they vanished from the previous time standards used in the countries from Mumbai and Kolkata.

Now, Indian Standard time 82 degrees approximately passes through the Mirzapur a city in UP.

Since India uses only IST therefore it does not consist of multiple time standards like other countries where they observe time standards based upon areas.

Here, In India people from every state are considered as citizens of a single country, unlike the US where people from different states observe separate time standards.

Although few parts of Assam still have a sub-set of time usually called Bagani Time zone.

IST remains the same throughout the year in India and Sri Lanka irrespective of the weather conditions like summer/winter. Though the government is proposing separate time zones for eastern states in India the same is not closed.

Multiple committees were formed to divide the country into different time zones in India, no feasible results were declared by them. IST still helps India to move forward along with international time zones.

Main Differences Between CST and IST 

  1. Territories: CST timeclock is observed at almost 9 territories namely the US, Canada, Mexico, and other states of North and Central America whereas IST time clock is followed in Asian territories of India and Sri Lanka.
  2. Dual Time zone: CST, as followed in Northern and Central states of America, is not observed for daylight time saving and in summer CST is replaced by (CDT) Central Day Light Time, and no such dual time zones are followed in India in replacement of IST.
  3. Changing Clocks: In the CST observation area clocks reset on the 2nd Sunday of March which lasts till the first Sunday of November but no such clock changing activities are performed in IST observation areas.
  4. Illustration example: As per the CST to IST conversion 9:00 AM CST time on Friday is 8:30: PM IST on Friday which depicts the 11 hours 30 minutes difference by referring to GMT.
  5. UTC Comparison: To equate time with UTC(Universally Coordinated Time) the CST needs a deduction of 6 hours in its current time, in contrast, IST needs the addition of Five Hours and Thirty Minutes with UTC.
  1. https://www.jstor.org/stable/24100281
  2. https://www.jstor.org/stable/3809288

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