datetime to string with time zone

I have a DateTime stored in universal time (UTC) of value 2010-01-01 01:01:01.

I would like to display it in EST in this format 2010-01-01 04:01:01GMT-04:00, however the 'K' formatter for timezone doesn't work in ToString

Use the "zzz" format specifier to get the UTC offset. For example:

        var dt = new DateTime(2010, 1, 1, 1, 1, 1, DateTimeKind.Utc);
        string s = dt.ToLocalTime().ToString("yyyy-MM-dd HH:mm:ss \"GMT\"zzz");
        Console.WriteLine(s);

Output: 2009-12-31 19:01:01 GMT-06:00

I'm in the CDT timezone. Make sure the DateTime is unambiguously DateTimeKind.Utc.

If like myself you happen to need a format like 2018-03-31T01:23:45.678-0300 (no colon in the timezone part), you can use this:

datetime.ToString("yyyy-MM-ddTHH:mm:ss.fffzzz").Remove(26,1)

This method will return the specified time in Eastern Standard Time (as the question requested), even if EST is not the local time zone:

public string GetTimeInEasternStandardTime(DateTime time)
{
	TimeZoneInfo easternStandardTime = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");
	DateTimeOffset timeInEST = TimeZoneInfo.ConvertTime(time, easternStandardTime);
	return timeInEST.ToString("yyyy-MM-dd hh:mm:ss tt\" GMT\"zzz");
}

Note: I haven't tested this in a non-English OS. See the MSDN documentation on TimeZoneInfo.FindSystemTimeZoneById.

Something like this works. You could probably clean it up a bit more:

string newDate = string.Format("{0:yyyy-MM-dd HH:mm:ss} GMT {1}", dt.ToLocalTime(), dt.ToLocalTime().ToString("%K"));

I think you are looking for the TimeZoneInfo class (see http://msdn.microsoft.com/en-us/library/system.timezoneinfo_members.aspx). It has many static methods to convert dates between time zones.