Convert CST to GMT Central Standard Time ↔ Greenwich Mean Time Free Online Secure
Type a time in CST and read it in GMT straight away. The offset is +6 h, the arithmetic wraps at midnight, and the answer says which day it lands on.
Nothing uploaded
Through the day — Convert CST to GMT (Central Standard Time ↔ Greenwich Mean Time)
| CST | GMT |
|---|---|
| 00:00 | 06:00 |
| 03:00 | 09:00 |
| 06:00 | 12:00 |
| 09:00 | 15:00 |
| 12:00 | 18:00 |
| 15:00 | 21:00 |
| 18:00 | 00:00 |
| 21:00 | 03:00 |
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.
Central time on the page, Greenwich time in the head
A booking confirmation from Nashville says doors open at 7:00 p.m. CST. A trade show in Dallas lists the first keynote at 9:00 a.m. CST. A manufacturing plant in Kansas City announces a shift change at 2:00 p.m. CST. If you work to the Greenwich clock, whether because you live in Britain or because your systems are set to GMT, you must convert CST to GMT before any of these makes sense. Add six hours: 7:00 p.m. CST is 01:00 GMT on the following day, 9:00 a.m. CST is 15:00 GMT, and 2:00 p.m. CST is 20:00 GMT.
This page shows the addition, lists reference tables, describes the two clocks, explains the four weeks each year when you must add only five hours, and runs through situations from country music to economic releases. The calculation takes place in your browser and nothing you type is sent to a server.
The sum behind a “convert CST to GMT” calculation
Add six to the Central hour
CST is UTC−6 and GMT is UTC+0, so Greenwich is six hours ahead. Express the Central time on a 24-hour clock and add six whenever you convert CST to GMT. If the total reaches 24 or more, subtract 24 and move to the next date. 21:15 CST plus six is 27:15, so the result is 03:15 GMT the following day.
Eight rows for reference
00:30 CST is 06:30 GMT. 06:15 CST is 12:15 GMT. 09:00 CST is 15:00 GMT. 12:00 CST is 18:00 GMT. 15:45 CST is 21:45 GMT. 18:00 CST is 00:00 GMT the next day. 21:30 CST is 03:30 GMT the next day. 23:45 CST is 05:45 GMT the next day. The first four stay on one date and the last four do not.
The 6 p.m. threshold
At 18:00 in Chicago it is midnight in Greenwich. Anything in the Central evening after that point is already tomorrow in London. A date mismatch is the commonest error, and this single landmark prevents it.
Central Standard Time, who uses it
The heartland
CST is the winter clock of Chicago, Dallas, Houston, San Antonio, Austin, Minneapolis, Kansas City, St. Louis, Memphis, Nashville, New Orleans, Milwaukee and Winnipeg, among many others. It also applies in most of Mexico and, all year, in Guatemala, Honduras, El Salvador, Nicaragua and Costa Rica and the Canadian province of Saskatchewan.
The summer variant
From the second Sunday in March to the first Sunday in November the United States and Canada observe Central Daylight Time, CDT, at UTC−5. Mexico stopped its summer time in 2022. The consequence is that a Mexican partner and a Texan partner agree on the time in winter but differ by an hour in summer.
Greenwich Mean Time as the destination
Britain’s winter clock
Britain and Ireland keep GMT from the last Sunday of October to the last Sunday of March. In the other half of the year they are on British Summer Time, UTC+1. Iceland and some West African countries stay on GMT all year. For programmers, GMT is also the label in HTTP headers and many logs for the reference time that coincides with UTC.
Why it works as a common ground
A time stated in GMT does not depend on whose summer-time law is in force. A reader in Dublin, Accra or Reykjavik sees the same hours as a reader in Edinburgh in winter. That is why international organisers often publish in GMT or UTC and leave the last step to the reader.
Other CSTs
CST also stands for China Standard Time (UTC+8) and Cuba Standard Time (UTC−5). Here it always means the North American Central zone.
Six hours across a working day
The shared window
Picture two office days on one Greenwich dial. The Central team sits at its desks from 15:00 to 23:00, and the London team from 09:00 to 17:00. The strip where both are present runs from 15:00 to 17:00, which on the Chicago wall is 09:00 to 11:00. Two hours is enough for a daily stand-up but leaves little room for a long workshop.
Who answers first
A message sent from Houston at 10:00 CST arrives at 16:00 GMT, with an hour of the British working day left, so a same-day reply is possible. The same message at 14:00 CST arrives at 20:00 GMT, and the answer comes the next morning.
Heading east by air
A night flight from Chicago to London that leaves at 18:00 CST, or midnight GMT, and takes seven hours lands at 07:00 GMT. The passenger arrives for breakfast after a short night, with the body clock at 01:00.
When it is five hours, not six
Two calendars for one ocean
The American spring change comes earlier than the European one and the American autumn change comes later. In 2026 the Central states switch on 8 March and 1 November. Britain switches on 29 March and 25 October. The gaps between those dates are the source of every five-hour exception.
Counting the exceptions
For three weeks from 8 March, a Chicago clock reads CDT while London is still on GMT, so Greenwich is only five hours ahead. For one week from 25 October, London has returned to GMT but Chicago has not, and again the lead is five hours. That adds up to four weeks, and in every other week the lead is six: CST against GMT in winter, CDT against BST in summer.
Adjusting the answer
The calculator above adds six hours. If your date is inside one of the four weeks, subtract an hour from what it shows. For instance, 11:00 CDT on 19 March corresponds to 16:00 GMT, not 17:00.
Country music in Nashville and Memphis
Doors, shows and radio
Concert listings in Nashville and Memphis give local times. A show that starts at 8:00 p.m. CST begins at 02:00 GMT on the following date. The famous Saturday night radio broadcast from the Grand Ole Opry starts at 7:00 p.m. CST, which is 01:00 GMT on Sunday. British fans who listen online therefore catch the evening in the small hours.
Tickets and travel
When the venue prints “doors 6:30 p.m.”, that is 00:30 GMT. A British visitor who booked a return flight leaving at 07:00 GMT the next morning should work out whether the late show leaves time to reach the airport. A quick convert CST to GMT before buying tickets answers the question.
Economic releases and the Central morning
Eastern-time announcements
Major United States statistics are released at 8:30 a.m. Eastern, which is 7:30 a.m. CST and 13:30 GMT. A trader in Chicago must be at a desk by 7:30, while a colleague in London who needs to convert CST to GMT sees the release in the early afternoon.
Central bank speeches
The Federal Reserve Bank of Chicago and its counterparts in Dallas and St. Louis publish speeches and data in Central time. A speech scheduled for 11:30 a.m. CST starts at 17:30 GMT. Analysts in Europe who read the transcript the next morning should check the timestamp on the document first.
Shift work in Midwestern factories
Three shifts, six hours apart from Greenwich
A plant in Kansas City runs shifts at 6:00 a.m., 2:00 p.m. and 10:00 p.m. CST. In Greenwich those hours are 12:00, 20:00 and 04:00. A supplier in Britain that monitors deliveries must know that the late shift, at 04:00 GMT, begins in the small hours of the British night.
Shift handovers
When a plant in Britain hands production data to a plant in the Midwest, the handover is often done at 14:00 GMT, which is 08:00 CST. A clean timeline in GMT lets both sites compare output without arguing about whose clock was used.
Football in the Lone Star State
Kick-off times
Professional games in Dallas and Houston often start at noon or 3:25 p.m. CST on Sundays, which is 18:00 or 21:25 GMT, and at 7:15 p.m. CST on Thursdays, which is 01:15 GMT on Friday. British followers of the sport adjust their weekends accordingly.
What the converter shows
The computation is exactly the one you do whenever you convert CST to GMT: add six hours to the local start time and check whether midnight has passed. The two examples that cross midnight are the ones that put the result on a different date.
Ports and pipelines on the Gulf coast
Houston and Galveston
Tankers and container ships dock at Gulf ports according to local schedules. A berth booked for 05:30 CST is booked for 11:30 GMT. A pilot boarding at 21:00 CST boards at 03:00 GMT the next day. A European charterer must keep both clocks in mind when reading a port notice.
Weather warnings
Gulf storms bring advisories several times a day. A notice effective until 4:00 p.m. CDT in summer expires at 21:00 UTC, or 22:00 BST. The label CDT, not CST, is the key to the correct sum in that season.
Streaming, podcasts and weekly shows
When it goes live
A weekly show that starts at 8:00 p.m. CST on Tuesday begins at 02:00 GMT on Wednesday. A morning podcast published at 6:00 a.m. CST appears at 12:00 GMT, shortly before the British lunch break. For regular listeners, a note in the diary prevents confusion.
Counting the minutes
Recordings that mention “this morning” or “tonight” need a time stamp. If you transcribe them, add the “convert CST to GMT” calculation step to every stamp before putting them in a single timeline.
Every hour in one table
CST to GMT
00:00 CST becomes 06:00 GMT. 01:00 CST becomes 07:00 GMT. 02:00 CST becomes 08:00 GMT. 03:00 CST becomes 09:00 GMT. 04:00 CST becomes 10:00 GMT. 05:00 CST becomes 11:00 GMT. 06:00 CST becomes 12:00 GMT. 07:00 CST becomes 13:00 GMT. 08:00 CST becomes 14:00 GMT. 09:00 CST becomes 15:00 GMT. 10:00 CST becomes 16:00 GMT. 11:00 CST becomes 17:00 GMT. 12:00 CST becomes 18:00 GMT. 13:00 CST becomes 19:00 GMT. 14:00 CST becomes 20:00 GMT. 15:00 CST becomes 21:00 GMT. 16:00 CST becomes 22:00 GMT. 17:00 CST becomes 23:00 GMT. 18:00 CST becomes 00:00 GMT (next day). 19:00 CST becomes 01:00 GMT (next day). 20:00 CST becomes 02:00 GMT (next day). 21:00 CST becomes 03:00 GMT (next day). 22:00 CST becomes 04:00 GMT (next day). 23:00 CST becomes 05:00 GMT (next day).
How to read it
Each row pairs one Central hour with its Greenwich hour and says when the date changes. The rows were obtained by adding six hours, which is what the calculator does when you convert CST to GMT.
Ten readings with minutes
Examples
01:05 CST becomes 07:05 GMT. 03:20 CST becomes 09:20 GMT. 05:50 CST becomes 11:50 GMT. 07:35 CST becomes 13:35 GMT. 10:10 CST becomes 16:10 GMT. 13:25 CST becomes 19:25 GMT. 16:40 CST becomes 22:40 GMT. 19:55 CST becomes 01:55 GMT (next day). 22:15 CST becomes 04:15 GMT (next day). 23:05 CST becomes 05:05 GMT (next day).
No change to the minutes
Since the difference is a whole number of hours, the minutes stay the same. If they change in your result, check your input.
What time of day is it?
Greenwich hours and the Central day
06:00 CST becomes 12:00 GMT (around midday). 08:00 CST becomes 14:00 GMT (afternoon). 10:00 CST becomes 16:00 GMT (afternoon). 12:00 CST becomes 18:00 GMT (evening). 14:00 CST becomes 20:00 GMT (evening). 16:00 CST becomes 22:00 GMT (night). 18:00 CST becomes 00:00 GMT (night). 20:00 CST becomes 02:00 GMT (night). 22:00 CST becomes 04:00 GMT (night).
Using the list
The words in brackets describe the part of the day in the Central zone. Use them to avoid proposing a call at an inconvenient hour.
Other American zones from Greenwich
The ladder
To reach GMT, add five hours to Eastern time, six to Central, seven to Mountain and eight to Pacific; Alaska needs nine and Hawaii ten. Someone who says “Eastern” means five, not six.
One moment, four clocks
When it is 10:00 in Chicago, it is 11:00 in New York, 09:00 in Denver, 08:00 in Los Angeles and 16:00 in Greenwich. Writing all five in an invitation spares readers a separate convert CST to GMT.
Dated examples for four seasons
A January Tuesday
At 11:00 CST on 13 January, Greenwich reads 17:00. Nobody is on summer time, so six hours apply.
A March Thursday
At 11:00 on a Chicago clock on 19 March, the label is CDT, and Greenwich reads 16:00. Only five hours separate them because America has moved and Britain has not.
A July Tuesday
At 11:00 CDT on 28 July, a London clock reads 17:00 BST. Both countries are on summer time, so six hours separate them again.
An October Tuesday
At 11:00 CDT on 27 October, Greenwich reads 16:00 GMT. London turned its clocks back two days earlier, but Chicago waits until 1 November, so five hours apply.
Checklist: how to convert CST to GMT
Before
Read the label
CST is standard time, CDT is daylight time, CT is either. For CT, look at the calendar.
Check the country
CST may also mean China or Cuba. Here it means the North American Central zone.
After
Add six hours
If the sum passes 24:00, subtract 24 and move to the next date.
Check the threshold
18:00 CST must come out as midnight GMT.
Overnight trains through the Mississippi valley
Long-distance schedules
Passenger trains that run between Chicago, Memphis and New Orleans publish timetables in local time. Say a sleeper leaves Chicago at 8:00 p.m. CST, which is 02:00 GMT, and reaches New Orleans at 7:30 a.m. CST the following day, which is 13:30 GMT. A rail enthusiast following the journey from Britain needs a “convert CST to GMT” calculation for each stop to see it in a single timeline.
Why the date matters
An overnight service crosses midnight in Chicago and also crosses it in Greenwich, but six hours apart. The same train is on one date by the Central clock and on another by the Greenwich clock for part of the journey.
University lectures and exams in the Midwest
Online sessions for British students
A lecture starting at 10:00 a.m. CST starts at 16:00 GMT, which suits British evening students. A seminar at 4:00 p.m. CST starts at 22:00 GMT and usually has a recording. A final exam set for 8:00 a.m. CST begins at 14:00 GMT, so a student in Britain must be ready for an afternoon paper.
Deadlines
An essay due at 11:59 p.m. CST on a Friday is due at 05:59 GMT on Saturday. Students in Britain who finish at 04:00 GMT on Saturday still make the cut-off, as long as they remember to convert CST to GMT correctly.
Mistakes when you convert CST to GMT
Taking away instead of adding
Greenwich is ahead of Chicago. A result smaller than the starting time means the sign was wrong, and you need to convert CST to GMT again.
Applying the Eastern number
Five hours is the Eastern figure. For the Central zone the figure is six.
Dropping the date change
A show announced for Saturday at 8:00 p.m. CST begins on Sunday at 02:00 GMT.
Treating Mexico like Texas
Mexico City keeps its clock fixed all year, so in the summer months it trails Texas by an hour.
Frequently asked questions
By how much do CST and GMT differ?
By six hours, with Greenwich in front.
Which formula do I use to convert CST to GMT?
Central hour plus six, and subtract 24 if the total is 24 or more.
How much is 3:00 p.m. CST in GMT?
21:00 GMT.
When is the difference five hours?
When North America is on summer time and Britain is not, which in 2026 means 8 to 28 March and 25 to 31 October.
Does the page keep what I type?
No. Everything happens inside your browser.
Related time zone converters
You might also want Convert CST to PST, Convert CST to EST, Convert UTC to GMT, Convert EET to GMT, Convert GMT to EET, Convert EST to CST, Convert PST to UTC, Convert EET to CST, Convert PST to EET. For the opposite direction, use Convert GMT to CST.
In brief, to convert CST to GMT you add six hours, remember the 6 p.m. threshold and allow for the four weeks of the year in which the gap is five. The calculation never leaves your device and requires no account.