# How to create datetime from day of year?

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Bruce Elliott on 24 Sep 2015
Commented: Peter Perkins on 25 Sep 2015
I know that I can get a date from a datetime object as YYYY-DDD, but what if I want to create a datetime object, given the year and day-of-year?
I've done this: >> T = datetime(2015,1,1) + days(266);
but is there a more direct way?

#### 1 Comment

Peter Perkins on 25 Sep 2015
It's worth noting that as long as you don't opt into time zones, the above works, but in general what you'd want is datetime(2015,1,1) + caldays(266). day(1) is just another way of saying hours(24), whereas caldays(1) is really "one day on the calendar" and accounts for daylight saving changes.

Steven Lord on 24 Sep 2015
The day, month, and year numbers you input into DATETIME don't need to be within the normal ranges for those numbers (1 to 12 for month, 1 to 28/29/30/31 for day depending on the month, etc.) For instance, September 24th 2015 is the 267th day of the year.
>> datetime(2015, 1, 267)
ans =
24-Sep-2015
There is some precedence for this, including some in MATLAB itself.
A = magic(4);
A(5) % A only has 4 rows but this linear index wraps around and refers to A(1, 2)

#### 1 Comment

Bruce Elliott on 25 Sep 2015
Thanks, Steven! I should have guessed that would work.
Thanks for the links, as well - also excellent references. ;-)