Question

Calling Date.today in Ruby returns the current date. However, what timezone is it in? I assume UTC, but I want to make sure. The documentation doesn’t state either way.

Answer 1

TL;DR: Date.today uses the system’s local time zone. If you require it be in UTC, instead get the date from a UTC time, e.g. Time.now.utc.to_date.

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Dates do not have timezones, since they don’t represent a time.

That said, as for how it calculates the current day, let’s look at this extract from the code for Date.today:

time_t t;
struct tm tm;
// ...
if (time(&t) == -1)
  rb_sys_fail("time");
if (!localtime_r(&t, &tm))
  rb_sys_fail("localtime");

It then proceeds to use use tm to create the Date object. Since tm contains the system’s local time using localtime(), Date.today therefore uses the system’s local time, not UTC.

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You can always use Time#utc on any Time convert it in-place to UTC, or Time#getutc to return a new equivalent Time object in UTC. You could then call Time#to_date on that to get a Date. So: some_time.getutc.to_date.

If you’re using ActiveSupport’s time zone support (included with Rails), note that it is completely separate from Ruby’s time constructors and does not affect them (i.e. it does not change how Time.now or Date.today work). See also ActiveSupport extensions to Time.