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 FileMaker Pro Custom Functions

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WeekDateISO ( date )

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  Average rating: 4.0  (40 votes)
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Michael Horak, *COMMENT Visual Realisation

Returns date in extended ISO 8601 week date format.

Sample Input:
Jan 2, 2005
Jan 3, 2005
Sample Output:

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


Returns date in extended ISO 8601 week date format.

The International Standard ISO 8601 extended format representation of week dates is yyyy-Www-d, where W is the actual letter "W", ww refers to the two digit week number, and d is the day's number.

Weeks are represented by two digits beginning with 01 being the first week of the year, up to 52 or 53 being the last week of the year. The first week of a year is the first week that contains four or more days of that year. Weeks start with Monday.

Days are represented by a single digit beginning with 1 being Monday, ending with 7 being Sunday.

This function is not recursive.

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


Hi Michael,

what a nice function! I don't dare giving you my previous calculation, it was such a mess compared to yours.

I'm now looking for the reverse function : give a ISO week number and year, and get a date (or a list of dates).
If by chance you have such a thing ready...

Many thanks,

Fabrice Nordmann, Brussels
December 02, 2010 6:04am

Hi Fabrice,

it shouldn't be very difficult. Hint: January 4 is ALWAYS within week 01.

comment, VR
December 02, 2010 8:02am

So simple indeed!
Thanks !

Fabrice Nordmann, Brussels
December 02, 2010 8:09am

Here's the reverse calculation:

Let (
jan4 = Date ( 1 ; 4 ; ISOyear )
jan4 - Mod ( jan4 - 1 ; 7 ) + 7 * ( ISOweek - 1 ) + ISOweekDay - 1

comment, VR
December 25, 2011 6:39pm

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