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GMT & UTC Time Explanation

What is GMT or UTC time?

GMT (Greenwich mean time) or UTC (coordinated universal time) are also sometimes called World Time. These represent a world standard of time.

Greenwich mean time was based upon the time at the zero degree meridian that crossed through Greenwich England. GMT became a world time and date standard because it was used by Britain's Royal Navy in the nineteenth century.

GMT or UTC use a 24-hour time format. "1:00 a.m." in GMT is expressed as 0100, 30 minutes after 0100 is expressed as 0130 (pronounced "zero one thirty").

The day begins at 0000(Zero Hundred) and ends with 2359 (11:59)

Examples
0000 Midnight
0800 8:00 am
1200 Noon
1430 2:30 pm

US conversion chart (C-1)

EDT = Eastern Daylight Time. EST = Eastern Standard Time.
CDT = Central Daylight Time CST = Central Standard Time
MDT = Mountain Daylight Time MST = Mountain Standard Time
PDT = Pacific Daylight Time PST = Pacific Standard Time

The Date is also included in the time.

The time calculation is based on your time zone and time of the year. GMT or UTC does not change with the seasons. The time where you live is always based on a subtraction of hours from GMT. This means that the date could also change.

How to calculate the date

The time is for the previous day if the GMT time is
less than the values shown for your time zone.

Atlantic Standard: 0400
Atlantic Daylight: 0300
Eastern Standard: 0500
Eastern Daylight: 0400
Central Standard: 0600
Central Daylight: 0500
Mountain Standard: 0700
Mountain Daylight: 0600
Pacific Standard: 0800
Pacific Daylight: 0700
Alaskan Standard: 0900
Alaskan Daylight: 0800
Hawaiian Standard: 1000

Fig 1

Example of a date change:

If you lived in the Eastern time zone during daylight savings time and the GMT time is 0300  on 8/10 then the time is actually on the evening of the 8/9.

Let's imagine it is 0300GMT

0300GMT = 11 PM according to the chart above (C-1).

fig. 1 tells us if the time is before 0400 Eastern Daylight that the date is on the previous day.

so the local time would be 11pm on 8/9.

Click Here to use a time conversion calculator.

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