CDT – Central Daylight Time


Understanding the time standard and time zones is useful if you work, communicate, or collaborate with people who live in different countries than you. Knowing how time zones work and how to calculate time in different locations around the planet helps you plan and communicate better – after all, no one wants to get a work call or a Zoom invitation for midnight or two in the morning, even though it may be a perfectly reasonable time on your end! 

To clear up the confusion about time zones, explain CDT (Central Daylight Time), one of the major time zones in the world, we’ll dig into the science and history behind time zones and talk about how it works. Next up, we will provide a list of the major territories that are located in the CDT time zone, as well as all the major cities in this region. And to make time zones more fun, we’ll list some curious time zone facts and trivia at the end of the article, so be sure to read it till the end.

Ready to start keeping world time? Let’s dive right in:

What Is a Time Zone?

To start at the beginning, let’s explain what a time zone really is. Because the Earth is a sphere that rotates, it cannot be noon at the same time all over the world: as the Earth turns, the sun hits different regions at different times. When it’s evening in London or Frankfurt, the sun is only rising in Lima or Los Angeles; in other words, different regions of the world observe noon at a different time, and when it’s night in one region, it may be noon in another. 

To keep track of time around the world accurately, scientists split the planet into 24 slices, each slice accounting for 15 degrees of longitude counting from the Greenwich Meridian, also known as longitude zero. Each slice is a time zone that is 15, 30, 45, and so on degrees West or East from Greenwich; one slice accounts for one hour behind or ahead the Greenwich Mean Time (GMT), which sits atop the zero longitude. This way, it’s 12PM at noon everywhere in the same time zone.

Now, time zones are calculated by degrees West or East rather than North or South. This is because, once again, the Earth rotates around its axis, but the poles do not move. What this means is that it’s noon everywhere along the same longitude: it’s the same time in Madrid and Cape Town, despite these cities being thousands of miles away from each other. However, if the countries are located West or East of each other, they will observe a different time – this is why Spain and Russia, as an example, are in different time zones despite being much closer than Spain is to South Africa.

This may sound confusing at first, but keeping time this way offers a lot of benefits to people, companies, and even the military around the globe. As long as you know which time zone you are in and the UTC offset of another country, you can easily calculate the time in that country. To make it even clearer, let’s talk about UTC and the UTC offset for a bit.

What Is CDT Time?

Central Daylight Time (CDT) is a Daylight Saving Time zone that is also known as CDST (short for Central Daylight Saving Time) or NACDT (short for North American Central Daylight Time). And, as you’ve probably guessed it already, the CDT time zone covers large parts of the United States and North America. As was stated earlier, CDT is UTC-05:00. In other words, it has an UTC offset of 5 hours (CDT is 5 hours behind UTC). And because it is a Daylight Saving Time, CDT is only used during the summer months. In the winter, many of the territories covered by CDT switch to the CST (Central Standard Time) time zone.

Why do some countries around the world switch to Daylight Savings time, while others do not? In essence, moving the clocks forward and back in the spring and fall months is done to extend the daylight hours. During summer, the sun rises and sets later, which is why moving the time forward by one hour helps extend the daylight giving people more daylight hours and saving energy. In the fall, the sun begins to rise and set earlier, and that’s when clocks are moved one hour back to account for the difference.

However, not all countries around the world use daylight savings. This largely depends on their proximity to the equator: on the equator, the day always has 12 light hours and 12 dark hours, so for countries like Ecuador, there’s simply no need to move the clocks. In the Northern and Southern Hemisphere, however, the difference between the length of day in summer and winter is more pronounced, which is why most countries further away from the equator observe Daylight Savings time seasonally. Curiously, some countries haven’t quite agreed on observing Daylight Savings: in Australia, for example, some states switch to summer time while others do not, no doubt creating some confusion.

Although in the West, the daylight savings tradition is only about a hundred years old – the DST changes were first introduced in Germany and Canada at the beginning of the 20th century – the practice in itself isn’t new. Ancient Romans seem to have made use of daylight savings, too: history shows Romans used water clocks with different scales to adjust for different solar time throughout a year. 

Brief History of CDT

Unlike other time zones such as UTC or EST that have a long history, it hasn’t been so long since the world was introduced to the concept of Central Daylight Time (CDT). The reason is that CDT is not a usual time zone. Instead, as we already mentioned, CDT is used only in certain months and only in the Americas. Therefore, it’s more like an additional time zone than the major one. 

This alternative time zone originates in 2007 and is exclusively used in North America and some parts of Canada. However, there are still many areas in both countries that refuse to use CDT for stabilizing time during the summer.

For example, in Canada, the Western province of Saskatchewan doesn’t accept the seasonal change. The reason is that the province is closer to the Mountain Time Zone’s meridian geographically and they don’t need to switch to a different time zone to adjust the time. Instead, they decided to be a part of the Central Time Zone and chose a permanent daylight saving system, consequently. However, the city of Lloydminster refuses the idea of Central Time and uses Mountain Time with DST.

Moreover, Mexico also refused to adapt to the change. However, in December 2009, the Mexican Congress changed its opinion and let ten cities that are located at the borders switch to the CDT time schedule in 2010 according to the US standards. 
But these are just some of the many exceptions that we’ll review below. The first time when North America started using Central Daylight Time was in 2007 when the local time changed from 2:00 local standard time to 3:00 local daylight time. Since this time, it usually happens on the second Sunday in March and returns back to the standard time on the first Sunday of November.

How Does CDT Work?

Even when people understand the importance of using CDT, sometimes it’s hard to adapt to its mechanism and find out how the CDT actually works. The only obvious thing is that sometime in the spring we change our clocks so that we will save daylight time in the summer. But when exactly do people switch their clocks from 2 p.m. to 3 p.m?

In fact, most of the United States starts switching to central daylight time at 2 a.m. on the second Sunday in March. They return their clocks back to standard time on the first Sunday in November. Since different American states use different time zones, needless to say, that each time zone switches at a different time in the U.S. 

Accordingly, in the European Union, countries that accept the idea of CDT switch to the central daylight time on the last Sunday in March and return to the Universal Time (or the Greenwich Mean Time) on the last Sunday in October. Unlike the Americas, in the EU all the time zones change at the same time. 

CDT vs CST – Differences

First of all, CTD stands for Central Daylight Time while CST is Central Standard Time. CDT is exclusively a North American time zone that is used during Daylight Saving Time (DST) only from the second Sunday in March to the first Sunday in November. Unlike CTD, CST is used throughout all the remaining days except the days when CTD is used. 
The main reason why people often get confused about these two time zones is that they both refer to the central time zone. But they are not the same because they are used during different periods of the year. The main difference is that CDT is applied during daylight saving time and consequently, these two time zones differ with an offset of one hour. Other than this, CDT is exactly the same as CST. Both time zones exist at the same time and are a part of the standard time. However, they replace each other during some period of the year.

How to Convert CDT to Other Time Zones?

In order to convert CDT to other time zones, you should pay attention to the following details:

  • CDT is 5 hours behind the GMT (Greenwich Mean Time) and is used in North America.
  • CDT started at 2 a.m. on Sunday, 13 March in 2021.
  • CDT will end at 2 a.m. on Sunday, 7 November in 2021 and the clocks will be set one hour back. 

Now let’s see what CDT looks like in relation to other time zones.

  • CDT is 1 hour behind EDT (Eastern Daylight Time).
  • CDT is 1 hour ahead of MDT (Mountain Daylight Time).
  • CDT is 2 hours ahead of PDT (Pacific Daylight Time).

Consequently, in order to convert CDT to EDT you need to add one hour; To convert CDT to MDT you need to subtract one hour, and to convert CDT to PDT, you need to subtract two hours. 

Major Territories in CDT Time

There are many territories in the United States, Canada and Mexico that are encompassed by the CDT time zone. However, remember that most of these territories will switch to Central Standard Time during the winter months, as CDT is a Daylight Saving Time.

Here are the states in the United States what use CDT during summer and CST during winter:

  • Alabama
  • Arkansas
  • North-western part of Florida
  • Illinois
  • Indiana
  • Iowa
  • Kansas except some of its western counties
  • The Western part of Kentucky
  • Louisiana
  • The western part of Michigan
  • Minnesota
  • Mississippi
  • Missouri
  • Only the eastern parts of Nebraska
  • Only the northern and eastern counties of North Dakota
  • Oklahoma
  • Only the eastern parts of South Dakota
  • Only the western parts of Tennessee
  • Most of Texas
  • Wisconsin

In Canada, however, just 3 territories are mostly in the CDT time zone: most of Ontario, Manitoba and parts of Saskatchewan. There are also a lot of Mexican states that are in the CDT time zone during the summer:

  • Aguascalientes
  • Campeche
  • Chiapas
  • Coahuila
  • Colima
  • Distrito Federal
  • Durango
  • Guanajuato
  • Guerro
  • Hidalgo
  • Jalisco
  • León
  • Michoacán
  • Morelos
  • México
  • Nuevo León
  • Oaxaca
  • Puebla
  • Querétaro
  • Quintana Roo
  • San Luis Potosí
  • Tabasco
  • Tamaulipas
  • Tlaxcala
  • Veracruz
  • Yucatán
  • Zacatecas

Some other territories that are in the CDT time zone are: Belize, Costa Rica, El Salvador, Guatemala, Honduras, and Nicaragua. It is not officially known how many people live in the CDT time zone, but the estimates put this number at over 300 million, most of them in the United States. So whenever you’re trying to contact someone who lives in an area covered by the CDT time zone, it’s not just the time zone differences you need to calculate – depending on whether it’s summer or winter, there will be one hour difference.

Major Cities in CDT Time

Because it covers large parts of North America and Canada, there are many large metropolitan areas in the CDT time zone. Here are the most important of them:

  • Amarillo, Texas
  • Antigua, Guatemala
  • Austin, Texas
  • Baton Rouge, Louisiana
  • Birmingham, Alabama
  • Bloomington, Illinois
  • Cedar Rapids, Iowa
  • Chicago, Illinois
  • Dallas-Fort Worth, Texas
  • Des Moines, Iowa
  • Fargo, North Dakota
  • Grand Rapids, Manitoba
  • Guadalajara
  • Guatemala City, Guatemala
  • Houston, Texas
  • Iowa City, Iowa
  • Jackson, Mississippi
  • Kansas City, Missouri-Kansas
  • Lawrence, Kansas
  • Managua, Nicaragua
  • Memphis, Tennessee
  • Mérida, Yucatán
  • Mexico City
  • Milwaukee, Wisconsin
  • Monterrey, Nuevo León
  • New Orleans
  • Oklahoma City, Oklahoma
  • Panama City, Florida
  • Puebla City
  • Racine, Wisconsin
  • Regina, Saskatchewan
  • Sioux Falls, South Dakota
  • St. Louis, Missouri
  • San José, Costa Rica
  • San Luis Potosí City
  • San Pedro Sula, Honduras
  • San Salvador, El Salvador
  • Saskatoon, Saskatchewan
  • Springfield, Illinois
  • Tampico, Tamaulipas
  • Thompson, Manitoba
  • Wheaton, Illinois
  • Winnipeg, Manitoba

Exceptions in the United States

As you can see, the major part of the United States uses Central Daylight Time annually but there are some exceptions as well that don’t change their clocks from March to November. Some areas in the country differ from the average territories because they are split into different time zones. Therefore, there are some states that observe two different times at the same time. 

Here’s the list of exceptional territories in the United States in the terms of Central Daylight Time:

  • Alabama (Phenix City, Valley, Smiths Station, and Lanett) – the state uses Eastern Standard Time (EST) which is UTC – 5 hours. 
  • Florida – this state also uses the Eastern Standard Time (EST) except for Florida’s panhandle, including the city of Pensacola and Apalachicola River territories where CST and CDT are used.
  • Indiana – the southwestern and northwestern parts of Indiana remain in the Central and Daylight time zones while most of the state is in the Eastern time zone.
  • Kansas – the state (including Wallace, Sherman, Greeley, and Hamilton) doesn’t use CDT and CST.
  • Kentucky – the western half of the state uses CDT and CST while the rest observes Eastern Time.
  • Michigan –  Gogebic, Iron, Menominee, and Dickinson counties use CST and CDT while the rest observes Eastern Time. 
  • North Dakota – the south area of the Missouri river observes Mountain Time Zone (MST), while 75% of the state is in the Central Time Zone.
  • South Dakota – the western half of the state uses Mountain Time Zone (MST), and the eastern half uses Central and Daylight time.
  • Oklahoma – the entire state observes the Central Time except for the community of Kenton that unofficially uses MST.
  • Tennessee – the western and middle parts of the state use CST and CDT and the rest is in the Eastern Time Zone.
  • Texas – the state observes Central Daylight Time, except two counties – Hudspeth and El Paso that are in the Mountain Time Zone.

Interesting Facts About Time Zones

Now that you know everything there is to know about time zones and the CDT time zone, it’s time to read a few interesting and fun facts about time zones:

  • Central Daylight Time is, as its name suggests, a Daylight-Saving Time. Central Standard Time, on the other hand, is not. This means that while CDT is UTC-05:00, CST is just UTC-6:00. Don’t forget this when trying to schedule a call with someone in Texas or Alabama, especially if your own country does not observe Daylight Savings.
  • Saskatchewan, in Canada, does not change its time. In other words, this territory is under permanent daylight saving.
  • The change to CDT happens in the second Sunday of March, at 2 AM. The change back to CST happens on the first Sunday of November, at 2 AM.
  • There are time zones that have an offset that contains fractions of an hour. For example, Indian time is UTC+05:30. Another interesting thing to note is that India uses a universal hour all across its vast territory. So it’s always the same local hour everywhere in India. Nepal uses fractions of an hour in its UTC offset as well (Nepal time is UTC+05:45).
  • Not all territories advance their clock by one hour when transitioning to Daylight Saving Time. Lord Howe Island in Australia advances the lock by just 30 minutes instead of the usual hour.
  • Vladimir Putin deleted 3 of Russia’s 12 time zones. Now Russia has just 9 time zones, even though it is spread across no less than 12.
  • China has just one time zone (UTC+08:00), which makes this particular time zone very wide. In fact, it is the widest time zone on planet Earth, and it’s an agreement rather than a geographical reality.
  • Greenwich Mean Time (GMT) is the same as London time, but only during the winter. In summer, the United Kingdom observes Daylight Saving Time (GMT+01:00). And the British created GMT.
  • All over the world, Daylight Saving Time is now used in over seventy countries and the changes affect over one billion people every year. The exact dates of moving the clocks forward and backward change from country to country, but generally, it occurs in the months of March in the spring and October – November in the fall.
  • The idea of having a daylight savings time was first proposed in 1895 in New Zealand by an entomologist George Hudson who proposed that moving the clocks will give people more daylight hours after work. In 1916, the Germans had the same idea, but a different purpose: to save energy, and soon, the daylight savings time swaps were accepted in Canada and the US. 
  • Daylight savings time is irrelevant on the equator because of the Earth’s natural tilt. In the middle section of the planet, the daylight hours are about the same, so there is no point to move the clocks. Further North or South from the equator, however, the countries receive more or less daylight depending of the time of year, which is why it makes sense to move the clocks and have a little more daylight – this is especially important in the more Northerly territories where nights are long.