Daylight Saving Time Rules. Converting UT Times Into Your Time Zone

Daylight Saving Time (DST) Rules
Converting UT Times Into Your Time Zone

Daylight Saving Time (DST) Rules

Due to the variety of Daylight Saving Time enforcements, a uniform DST shift is applied on our site. One hour from April to October included, in the northern hemisphere. One hour from October to March included, in the southern hemisphere. Hence you may need some adjustments if your country enforces DST at a different period or if it does not

Equatorial and tropical countries do not have any Daylight Saving Time (DST) rules with days equaling nights all year long

Northern Hemisphere
Southern Hemisphere

Northern Hemisphere

Southern Hemisphere

Converting UT Times Into Your Time Zone

The GMT system in 1884 which was succeded about 1926 by the UT system, implemented a uniform international time system which is still in use. It is the famous 24 timezones system, with the Greenwich meridian as the prime meridian. The timezones are dividing the world into 15° wide zones, East or West of Greenwich, each centered on its central meridian. Each time zone is differing from Greenwich time by a certain amount of hours

USA
Other Countries (West of Greenwich)
Other Countries (East of Greenwich)

USA

UT is expressed in a 24 hour system and not in an a.m./p.m. system. I.e. hours are counted 0-24 from midnight to midnight, and from noon onwards (after 12:00 p.m.), 13, 14, 15 etc are used as figures instead of 1, 2, 3 p.m. etc: 1:00 p.m. is 13:00, 2:00 p.m. is 14:00, etc, midnight eventually being 0:00. Note, so, that, before noon, systems match. You will have to take this in account to understand your time conversions. To get US standard time zones, substract from UT 5 for EST, 6 for CST, 7 for MST, 8 for PST, and 9 for Alaska-Yukon and 10 for Hawai. When Daylight Saving Time is in effect, substract one hour less than these figures. In USA Daylight Saving Time begins on the first Sunday of April, 2:00 a.m. and ends the last Sunday of October, 3:00 a.m (in both cases these dates are not valid for Arizona, Hawaii and most of the counties of Indiana). If you get a negative figure, in each of all these cases, add 24 hours; hence the hour you get is for the day before the UT date/time you started from. E.g. if you have to convert 5:15 UT (for July, 8th) into PDT, you substract 7 from 5:15, i.e. you get -2:15; you add 24 as result is negative: -2:15 + 24 = 22:15; which translated from the 24 hours system into an a.m./p.m. one gives: 10:15 p.m. (22:00 is for 10:00 p.m.); and this time is one day before, i.e. 10:15 p.m. PDT, July, 7th as starting date was July, 8th. As, if you have to convert the same time/date into EDT, 5:15 UT being 5:15 a.m., you substract 4: 5:15 - 4 = 1:15; as the result is not negative, you are on the same day than the UT day you started from, i.e. you get 1:15 EDT, July, 8th, 1:15 being 1:15 a.m.

	Offset/UT (Standard Time)	Offset/UT (Dayling Saving Time)
Atlantic Standard Time Zone	-4	-3
Eastern Standard Time Zone	-5	-4
Central Standard Time Zone	-6	-5
Mountain Standard Time Zone	-7	-6
Pacific Standard Time Zone	-8	-7
Alaska-Yukon Standard Time Zone	-9	-8
Hawaii Standard Time Zone	-10	-9

Other Countries (West of Greenwich)

UT is expressed in a 24 hour system and not in an a.m./p.m. system. I.e. hours are counted 0-24 from midnight to midnight, and from noon onwards (after 12:00 p.m.), 13, 14, 15 etc are used as figures instead of 1, 2, 3 p.m. etc: 1:00 p.m. is 13:00, 2:00 p.m. is 14:00, etc, midnight eventually being 0:00. Note, so, that, before noon, systems match. You will have to take this in account to understand your time conversions, or, if your country is already using a 0-24 system do not change anything. Once you know the difference between UT and your country time zone (plus the possible daylight saving time period) just compute your local time using the same rules than for USA: substract the appropriate figure from the UT time. If the result is negative, add 24 hours (and hence the hour you get is for the day before the UT date/time you started from). E.g. if your country is shifted 6 (with or without Daylight Saving Time) from UT and you have to convert 5:15 (for July, 8th) to your local time, substract 6 from 5:15, i.e. -1:15; add 24 as result is negative: -1:15 + 24 = 23:15. Which is 23:15, or -translated into an a.m./p.m. system- 11:15 p.m. (23:00 is for 11 p.m.). This time is one day before, i.e. 23:15 or 11:15 p.m. your time, July, 7th (as starting date was July, 8th). If you have to convert 11:15 UT, July, 8th (the a.m./p.m. time for 11:15 UT is 11:15 a.m.) for the same time zone, substract 6 again: 11:15 - 6 = 5:15; as result is not negative, you are on the same day than the UT day you started from, i.e. you get 5:15 (which is always a.m. in an a.m./p.m. system) your time, July, 8th

Other Countries (East of Greenwich)

UT is expressed in a 24 hour system and not in an a.m./p.m. system. I.e. hours are counted 0-24 from midnight to midnight, and from noon onwards (after 12:00 p.m.), 13, 14, 15 etc are used as figures instead of 1, 2, 3 p.m. etc: 1:00 p.m. is 13:00, 2:00 p.m. is 14:00, etc, midnight eventually being 0:00. Note, so, that, before noon, systems match. You will have to take this in account to understand your time conversions, or, if your country is already using a 0-24 system do not change anything. Once you know the difference between UT and your country time zone (plus the possible daylight saving time period) just compute your local time by adding the appropriate figure to the UT time. If result is over 24, substract 24 hours (and hence the hour you get is for the day after the UT date/time you started from). E.g. if your country is shifted 7 (with or without Daylight Saving Time) from UT and you have to convert 19:15 (for July, 8th) to your local time, add 7 to 19:15, i.e. 26:15; as result is over 24, substract 24: 26:15 - 24 = 2:15. This time is one day after, i.e. 2:15 your time, July, 9th (as starting date was July, 8th) -or 2:15 a.m., July, 9th, in an a.m./p.m. system. If you have to convert 10:15 UT, July, 8th for the same time zone, add 7 again: 10:15 + 7 = 17:15; result is not over 24, you are on the same day than the UT day you started from. Time is 17:15 if your time system is a 0-24 one (or 5:15 p.m. if it is an a.m./p.m. system -17:00 is for 5 p.m.) your time, July, 8th. Note that in France, Daylight Saving Time (DST) is enforced from the last Sunday of March, 2:00 a.m. to the last Sunday of October, 3:00 a.m.