Develop Reference

Convert date from UTC to local timezone during daylight saving [duplicate]

I'm trying to use DateTimeOffset to convey a specific moment in time across any time zone. I can't figure out how to use TimeZoneInfo to deal with daylight saving time.
var dt = DateTime.UtcNow;
Console.WriteLine(dt.ToLocalTime());
var tz = TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time");
var utcOffset = new DateTimeOffset(dt, TimeSpan.Zero);
Console.WriteLine(utcOffset.ToOffset(tz.BaseUtcOffset));
This prints out:
6/2/2010 4:37:19 PM
6/2/2010 3:37:19 PM -06:00
I am in the central time zone, and and we are currently in daylight saving time.
I am trying to get the second line to read:
6/2/2010 4:37:19 PM -05:00
BaseUtcOffset apparently doesn't change based on DST.
How can I get the the right time with the proper offset value?

You can also use TimeZoneInfo.ConvertTimeFromUtc, which will allow for daylight saving time:
DateTime utc = DateTime.UtcNow;
TimeZoneInfo zone = TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time");
DateTime localDateTime = TimeZoneInfo.ConvertTimeFromUtc(utc, zone);

You need to get the UtcOffset from the TimeZoneInfo, then pass that to the ToOffset() method:
var dt = DateTime.UtcNow;
Console.WriteLine(dt.ToLocalTime());
var tz = TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time");
var utcOffset = new DateTimeOffset(dt, TimeSpan.Zero);
Console.WriteLine(utcOffset.ToOffset(tz.GetUtcOffset(utcOffset)));

Or better, if you don't want to hard code the time zone identifier:
TimeZoneInfo tzi = TimeZoneInfo.FindSystemTimeZoneById(TimeZoneInfo.Local.Id);
DateTime localDateTime = TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, tzi);

I'm a beginner both at .NET and stackoverflow, so I could be wrong, but here goes:
Using TimeZoneInfo.ConvertTimeFromUtc will allow for daylight saving time, and convert to the correct time according to the time zone + a possible DST offset. However - the offset itself in the resulting object will show the offset for standard time, and not take daylight saving time into account. So if you want to do a ToString on the object, you will end up with the correct time (in hours and minutes), but the wrong offset during daylight saving time, which may lead to the wrong moment in time later in the code.
If you instead use the GetUtcOffset to get the offset for a specific time, and then do a ToOffset on the DateTimeOffset object, both the hours/minutes and the offset itself will be correctly converted, and you can safely do a ToString.
string ExpectedDateTimePattern = "yyyy'-'MM'-'dd'T'HH':'mm':'ss''zzz";
string timeZoneId = "FLE Standard Time";
string dateTimestr = "2017-10-09T09:00:00+02:00";
DateTimeOffset dto = DateTimeOffset.Parse(dateTimeStr);
TimeZoneInfo zone = TimeZoneInfo.FindSystemTimeZoneById(timeZoneId);
TimeSpan offset = zone.GetUtcOffset(dto);
dto = dto.ToOffset(offset);
string localTime = dto.ToString(ExpectedDateTimePattern);
localTime will return "2017-10-09T10:00:00+03:00".
datetimeoffset timezoneinfo getutcoffset

This will Adjust automatically... and Return time as per your timezone.
public static string SetLastModified (
TimeZoneInfo csttzi = TimeZoneInfo.FindSystemTimeZoneById(TimeZone.CurrentTimeZone.StandardName);
DateTime cstTime = TimeZoneInfo.ConvertTime(DateTime.UtcNow, csttzi);
return String.Format("DaylightSavingTime: {0}", cstTime.IsDaylightSavingTime().ToString());
}

UTC DateTime to Local and Back gives incorrect time

I need to be able to convert UTC time to Local Time, add one hour and would like to convert back to UTC for comparison. However, the basic to TimeZone and back to UTC gives incorrect time.
DateTime utcDateTime = DateTime.SpecifyKind(DateTime.UtcNow, DateTimeKind.Utc);
var localTime = utcDateTime.ToZone("Central Time (US & Canada)"); // CORRECT TIME
// INCORRECT when converted back to utc. It should be the same as utcDateTime
var convertedBack = TimeZoneInfo.ConvertTimeToUtc(localTime);
What am I missing?

// This works
TimeZoneInfo tz = TimeZoneInfo.FindSystemTimeZoneById("Central Standard Time");
var convertedBack =TimeZoneInfo.ConvertTimeToUtc(localTime, tz);

Apply TimeZone to a specific date?

For example, server time is 11 pm.
User timezone, specified within the app, is US Mountain Standard Time.
So I need to get 4 pm, user time.
Tried with
var UserTimeZoneInfo = "US Mountain Standard Time";
var userTime =TimeZoneInfo.ConvertTimeToUtc(now, _UserTimeZoneInfo);
and this
var userTime = new DateTimeOffset(now, this._UserTimeZoneInfo.BaseUtcOffset);
but in both cases, I get 8am instead of 4pm. TimeZone difference gets added to server time , instead of subtracted. I see there are other DateTime functions, but not sure which one to use ?

You need to use ConvertTimeFromUtc method if you want change to specified timezone time from UTC.
var timeZone = TimeZoneInfo.FindSystemTimeZoneById("US Mountain Standard Time");
DateTime arizonaTime = TimeZoneInfo.ConvertTimeFromUtc(new DateTime(2017, 11, 9, 23, 0, 0,DateTimeKind.Utc), timeZone);
DotNetFiddle

You can use ConvertTime which Converts a time to the time in a particular time zone.
DateTime currentDt = DateTime.Now;
var timeZone = TimeZoneInfo.FindSystemTimeZoneById("US Mountain Standard Time");
var userTime = TimeZoneInfo.ConvertTime(currentDt, timeZone);

Handling Time over TimeZones

I am attempting to convert this string time value 2017-01-10T13:19:00-07:00 to local time (Eastern). Now from my research 07:00 is Mountain Time which is 2 hours beind Eastern Time (my local). However, when I run this syntax to convert the returned output is 01/17/2017 10:19:00 AM which is 3 hours difference, not 2.
This is my syntax I am using, is this set-up incorrectly? What should I change in order to have the accurate local time returned from the UTC time?
static void Main(string[] args)
{
string green = "2017-01-10T13:19:00-07:00";
DateTime iKnowThisIsUtc = Convert.ToDateTime(green);
DateTime runtimeKnowsThisIsUtc = DateTime.SpecifyKind(
iKnowThisIsUtc,
DateTimeKind.Utc);
DateTime localVersion = runtimeKnowsThisIsUtc.ToLocalTime();
Console.WriteLine(localVersion);
Console.ReadKey();
}
EDIT
I have verified my computer is set to the correct time zone by using the following syntax which produces Eastern for both (which is correct)
TimeZone zone = TimeZone.CurrentTimeZone;
string standard = zone.StandardName;
string daylight = zone.DaylightName;
Console.WriteLine(standard);
Console.WriteLine(daylight);

Convert the string to a DateTime object:
var datetime = DateTime.Parse("2017-01-10T13:19:00-07:00");
Get the timezone for EST:
var easternZone = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");
Convert to EST (note the conversion .ToUniversalTime()):
var easternTime = TimeZoneInfo.ConvertTimeFromUtc(datetime.ToUniversalTime(), easternZone);
Output of easternTime.ToString();:
10/01/2017 15:19:00
(I'm in the UK hence dd/MM/yyyy, yours may show differently)

// your input string
string green = "2017-01-10T13:19:00-07:00";
// parse to a DateTimeOffset
DateTimeOffset dto = DateTimeOffset.Parse(green);
// find the time zone that you are interested in.
// note that this one is US Eastern time - inclusive of both EST and EDT, despite the name.
TimeZoneInfo tzi = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");
// convert the DateTimeOffset to the time zone
DateTimeOffset eastern = TimeZoneInfo.ConvertTime(dto, tzi);
// If you need it, you can get just the DateTime portion. (Its .Kind will be Unspecified)
DateTime dtEastern = eastern.DateTime;

When your application needs to be unambiguously aware of timezones, you may want to consider a DateTimeOffset instead of DateTime.
Choosing Between DateTime, DateTimeOffset, TimeSpan, and TimeZoneInfo
And this question looks like someone has collected lots of best practices on this topoic - Daylight saving time and time zone best practices

How to handle UTC difference while converting DateTime

When I am trying to convert a date to AST and then convert it back to IST, why is there a difference of 1 hour?
var tesDate = DateTime.Parse("2015-09-01T03:30:00+05:30");
TimeZoneInfo tmz = TimeZoneInfo.FindSystemTimeZoneById("Atlantic Standard Time");
DateTime tesDate1 = DateTime.SpecifyKind(tesDate, DateTimeKind.Unspecified);
var earliestStartTime = TimeZoneInfo.ConvertTime(tesDate1, tmz, TimeZoneInfo.Utc);
//Local Time is Now in IS
var localEarliestStartTime = earliestStartTime.ToLocalTime();
Actual OutPut {9/1/2015 12:00:00 PM}
Expected Output {9/1/2015 01:00:00 PM}

When I am trying to convert a date to AST and then convert it back to IST, why is there a difference of 1 hour?
Because you're not actually doing that conversion. You're doing something much more convoluted, and I'm not sure why. I'll comment your code so you can see what you are doing:
// Parse a string with a fixed +05:30 Indian offset
// This is converting to the local time zone in the process (Kind == DateTimeKind.Local)
var tesDate = DateTime.Parse("2015-09-01T03:30:00+05:30");
// Get the Atlantic time zone
TimeZoneInfo tmz = TimeZoneInfo.FindSystemTimeZoneById("Atlantic Standard Time");
// Assign DateTimeKind.Unspecified, which removes the existing Local kind (why?)
DateTime tesDate1 = DateTime.SpecifyKind(tesDate, DateTimeKind.Unspecified);
// Convert to UTC, pretending the time is in AST, when actually it's in the local zone
var earliestStartTime = TimeZoneInfo.ConvertTime(tesDate1, tmz, TimeZoneInfo.Utc);
// Convert from UTC back to the local zone
var localEarliestStartTime = earliestStartTime.ToLocalTime();
This is a bit silly, and of course it will lead to the wrong values. If your goal is to convert from IST to AST and back, then you should just do this:
TimeZoneInfo tzAtlantic = TimeZoneInfo.FindSystemTimeZoneById("Atlantic Standard Time");
TimeZoneInfo tzIndian = TimeZoneInfo.FindSystemTimeZoneById("India Standard Time");
DateTimeOffset original = DateTimeOffset.Parse("2015-09-01T03:30:00+05:30");
DateTimeOffset atlantic = TimeZoneInfo.ConvertTime(original, tzAtlantic);
DateTimeOffset indian = TimeZoneInfo.ConvertTime(atlantic, tzIndian);
There's no need to involve either UTC or the local time zone, unless you have some other purpose that you didn't explain.