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 FileMaker Pro Custom Functions

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isDaylightTime ( dt )

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  Average rating: 4.4  (30 votes)
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Howard Schlossberg, FM Professional Solutions

Returns 1 or 0 to indicate whether the given date falls within U.S. daylight savings time (post-2007)

Sample Input:
isDaylightTime ( date( 5; 1; 2014 ) )
Sample Output:

 Then copy & paste into FileMaker Advanced's Edit Custom Function window.


Returns 1 or 0 to indicate whether the given date falls within U.S. daylight savings time (post-2007)

Note: these functions are not guaranteed or supported by Please contact the individual developer with any questions or problems.

This is my Custom Function and I want to edit it


There is a mistake in the DSTEnd calc., it should be identical to the DSTBegin calc except for the month/day values.

Instead of simply fixing it that way, I made the following modification

dow_oset = floor( mod( 1 + ( yr * 1.25); 7) );
DSTBegin = date( 3 ; 14 ; yr ) - dow_oset;
DSTEnd = date( 11 ; 7 ; yr ) - dow_oset

An interesting detail to note is DST is a constant at 238 days. Therefore DSTEnd can be obtained thusly:

DSTEnd = DSTBegin + 238

Additionally, there is a DayOfWeek function, so the following is equivallent

dow_oset = DayOfWeek(date(3, 1, yr))

Here is the entire rewrite:

yr = Year(dt);

// DSTBegin is 2nd Sunday of March, minimum is the 8th.
FirstPossibleSunday = Date(3; 8; yr);

// Offset to 2nd Sunday of March
DSTBegin = FirstPossibleSunday + (8 - DayOfWeek(FirstPossibleSunday))

dt < DSTBegin ; 0 ;
dt >= DSTBegin + 238 ; 0 ;

Scott, Edmonton, AB
April 29, 2015 8:49pm

Thanks for your notes, Scott. Yours is certainly easier to understand than mine, which I essentially copied from some forum I found online for some other computer language when I needed a solution for whatever I was working on at the time.

Meanwhile, I've fixed the missing floor() in my calc above, and visitors now have the option of using mine or yours.

Thanks again...

Howard Schlossberg, Los Angeles
April 29, 2015 9:15pm

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