U.S.A. Daylight Saving Time Starting / Ending Dates (Valid from 1986)
Year =

U.S.A. Daylight Saving Time Start / End Dates For 2017

Starts on the second Sunday in March and ends on the first Sunday in November.
Daylight Saving Time Starting Date

2017      March
SunMonTueWedThuFriSat
      1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30 31  

Daylight Saving Time Ending Date

2017      November
SunMonTueWedThuFriSat
      1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30    

Duration = 238 days = 34 weeks

In earlier times, Daylight Saving Time across the U.S.A. was inconsistent, starting and ending on various dates in different states, sometimes arbitrarily, according to the whims of the current governors.  So, when and where it was used, it was not used according to a uniform schedule.  These variable inconsistencies caused some interstate trade, commerce, recordkeeping, communications and other problems, so some federal laws were enacted to regulate its optional usage.

From 1986 to 2006, the basic rule was:

  • Each state may or not, at its option, observe daylight saving time.

  • All states that do opt to observe it, must do so according to a uniform federal schedule, starting on the first Sunday in April and ending on the last Sunday in October.

Under that rule, the duration of daylight saving time was sometimes 210 days (30 weeks) in some years or 203 days (29 weeks) in others.  Starting in 2007, a new rule went into effect.


From 2007 to the present, the rule is:

  • Each state may or not, at its option, observe daylight saving time.

  • All states that do opt to observe it, must do so according to a uniform federal schedule, starting on the second Sunday in March and ending on the first Sunday in November.

Under the new rule, daylight saving time starts two weeks earlier and ends two weeks later than before, adding four weeks or one more month of daylight saving time to the year than previously.  This is the rule for daylight saving time currently in effect in the United States.  Under this new rule, the duration of daylight saving time is always constant at 238 days (34 weeks).


On the date when Daylight Saving Time starts, it begins at 2:00 AM local time in each time-zone, at which time, the clocks are set ahead exactly one hour so that, at that moment, it becomes 3:00 AM instead.  The normally scheduled hour from 2:00 AM to 3:00 AM is skipped over or dropped so, in effect, one hour is lost from the clock that day and the next sunrise and sunset are suddenly one hour earlier than the day before.  It gets daylight/dark one hour earlier than previously.  Daylight saving time is now in effect.

On the date that Daylight Saving Time ends and we revert back to standard time, it begins at 2:00 AM local time in each time-zone, at which time the clocks are set back exactly one hour so that, at that moment, it becomes 1:00 AM - again.  The hour from 1:00 AM to 2:00 AM is repeated.  In effect, one extra hour is added to the clock that day and the next sunrise and sunset are suddenly one hour later than the day before.  It gets daylight/dark one hour later than previously.  Standard time is now back in effect.

With 2:00 AM being used as the transition time, there is never any confusion about the date after the transition either way since the date cannot change.

It is not entirely inconceivable that one day the Daylight Saving Time rule used in the U.S.A. will be changed to coincide with the Summer Time Rule used by the E.U. and some other countries.


Gov. Ref.
Excerpt from: Public Law 109-58 - 109th Congress of the United States of America
http://www.gpo.gov/fdsys/pkg/PLAW-109publ58/html/PLAW-109publ58.htm 

...

SEC. 110. DAYLIGHT SAVINGS.

(a) Amendment.
--Section 3(a) of the Uniform Time Act of 1966 (15 U.S.C. 260a(a))
  is amended--

(1) by striking "first Sunday of April" and inserting
"second Sunday of March"; and

(2) by striking "last Sunday of October" and inserting
"first Sunday of November".

(b) Effective Date.
--Subsection (a) <<NOTE: 15 USC 260a note.>> shall take effect 1 year
after the date of enactment of this Act or March 1, 2007, whichever
is later.

(c) Report to Congress.
--Not <<NOTE: 15 USC 260a note.>> later than 9 months after the effective
date stated in subsection (b), the Secretary shall report to Congress on
the impact of this section on energy consumption in the United States.

(d) Right to Revert.
--Congress retains the right to revert the Daylight Saving Time back to
the 2005 time schedules once the Department study is complete.

...

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