Date off by a month using Arcade

[BertKraan1]

A collegue used collector to record some records but a datefield wasn't filled. I decided to use arcade to fill the field:

But instead of May 11th I see June 10th. This is so confusing.

I understand that date is stored in utc but displayed in my local timezone (I'm near Amsterdam) so I was expecting some hours difference but this seems more than a month.

What am I doing wrong?

regards,

Bert

[KenBuja · Accepted solution]

When using the Date function, months are defined by 0-11 instead of 1-12.

month

Number

The month (0-11) where 0 is January and 11 is December.

[JonathanJew1]

Can anyone explain why the month() would be indexed at 0, while day() and year() actually returns what one would expect? Python treats months consistently, and I just can't wrap my head around why arcade would have been designed this way. 

[DanThompson]

yeah it makes no sense..

[bogrevy]

Although it is stated in the documentation for both the Date function and the Month function, it makes no sense at all that this is 0-based.

The problem with changing that is that any existing arcade expressions that use these functions will fail. I would still recommend Esri to change these features instead of continuing to bear the pain all the following years.