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Get time zone with UTC conversion

I have the system date in BST . I want to convert it to UTC. So did the below:
string utcDate= TimeZoneInfo.ConvertTimeToUtc(dt).ToString("dd/MM/yyyy HH:mm:ss");
What I want is to get the zone along with the Date in UTC. Pls consider the daylight savings.
Example: 2019-07-08T23:59:00+01:00.

A few things:
The string format you gave the example of, 2019-07-08T23:59:00+01:00 is part of the ISO 8601 specification. To be precise, it is the "complete date and time of day representation" of the "ISO 8601 Extended Format". It also the format defined by RFC 3339.
In this format, the date and time portion represent the local time, as denoted by the time zone offset portion. In other words, the values are not in UTC, but already adjusted. In your example, 2019-07-08T23:59:00 is the local time and UTC+01:00 is in effect at that time. The corresponding UTC time would thus be an hour earlier, 2019-07-08T22:59:00Z.
You seem to be asking for the date in UTC but with an offset that includes daylight saving time. That is impossible, as UTC does not observe daylight saving time. The offset from UTC is always zero. You can read more about UTC here.
The offset of UTC itself is denoted with Z, but can also be represented with +00:00, which can be thought of as "zero offset from UTC". In other words, if you are referring to UTC time use the Z, and if you are referring to a local time that is aligned to UTC (such as GMT in London in the winter, or Iceland, etc.) use +00:00.
In your question, you say you want the system time in UTC with the offset. I will assume by "system time" you mean the current time of the clock on the system. That is provided by DateTime.UtcNow or DateTimeOffset.UtcNow. These return either a DateTime or DateTimeOffset structure - not a string. Since you wanted a string in a specific format, then you should first ask for the current time, and then format it as a string with ToString:
using System.Globalization;
...
string a = DateTime.UtcNow.ToString("yyyy-MM-dd'T'HH:mm:ssK", CultureInfo.InvariantCulture);
// output example: "2019-07-08T22:59:00Z"
string b = DateTimeOffset.UtcNow.ToString("yyyy-MM-dd'T'HH:mm:sszzz", CultureInfo.InvariantCulture);
// output example: "2019-07-08T22:59:00+00:00"
If what you actually wanted was the local time, such that the offset would be +00:00 in the winter and +01:00 in the summer (in the UK), then use Now instead of UtcNow. This gives the local time in the time zone of the computer where the code is running.
string c = DateTime.Now.ToString("yyyy-MM-dd'T'HH:mm:ssK", CultureInfo.InvariantCulture);
// output example: "2019-07-08T23:59:00+01:00"
string d = DateTimeOffset.Now.ToString("yyyy-MM-dd'T'HH:mm:sszzz", CultureInfo.InvariantCulture);
// output example: "2019-07-08T23:59:00+01:00"
If you actually wanted the time in the UK regardless of what the time zone of the local computer was on, then you'd have to first get the UTC time and then convert it to UK time before creating the string.
TimeZoneInfo tzi = TimeZoneInfo.FindSystemTimeZoneById("GMT Standard Time");
string e = TimeZoneInfo.ConvertTime(DateTime.UtcNow, tzi).ToString("yyyy-MM-dd'T'HH:mm:ssK", CultureInfo.InvariantCulture);
// output example: "2019-07-08T23:59:00"
string f = TimeZoneInfo.ConvertTime(DateTimeOffset.UtcNow, tzi).ToString("yyyy-MM-dd'T'HH:mm:sszzz", CultureInfo.InvariantCulture);
// output example: "2019-07-08T23:59:00+01:00"
In example e, note that a DateTime can't store an arbitrary offset as the result of time zone conversion, and thus you get DateTimeKind.Unspecified assigned to the Kind property, which results in no offset being in the string representation. Thus most of the time you should use a DateTimeOffset (example f) instead.
Also, note the time zone ID of "GMT Standard Time" is the correct ID to use for the UK on Windows platforms. It correctly switches between GMT and BST when appropriate. If you are running .NET Core on non-Windows platforms (Linux, OSX, etc.), then you should use "Europe/London" instead. Or if you are wanting to write code that is platform-neutral then you can use my TimeZoneConverter library, which allows you to provide either form and run on any platform.
In your code example, you didn't call any of the "now" functions, but gave a dt variable. Assuming this is a DateTime, the result of calling TimeZoneInfo.ConvertTimeToUtc will depend on the Kind property of that variable. If it's DateTimeKind.Utc, then no conversion is performed. If it's DateTimeKind.Local or DateTimeKind.Unspecified, then the value is converted from the computer's local time zone to UTC.
Lastly, keep in mind that when talking to an international audience, time zone abbreviations can be ambiguous. I could deduce by "BST" that you meant British Summer Time, but only because you showed a +01:00 offset in your question. "BST" can also stand for "Bangladesh Standard Time" (+06:00), or "Bougainville Standard Time" (+11:00).

I guess you can do something like this:
var dt = DateTime.Now;
string utcDate = dt.ToUniversalTime().ToString("dd/MM/yyyy HH:mm:ss") +
dt.ToString(" zzz");
Output: (I'm in EET)
14/07/2019 20:02:17 +02:00
But be aware that this could be confusing to people. The standard way is that the timezone follows the local date, not the universal date.

How to get DateTime from UTC offset

I am trying to figure out how to get a DateTime instance using an UTC offset value, i have to get the DateTime of the desired UTC offset regardless of which UTC the current system is.
All posts i've seen are about getting the UTC string data from a DateTime, also i've seen that there is a post that says how to get the other DateTime by calculating the difference using the current DateTime, that doesn't seem to work well since i need the code to be working regardless of which UTC the system is using.
What i have tried this far:
public static void Main(string[] args) {
DateTime utcDateTime = DateTime.UtcNow;
TimeSpan offSet = TimeSpan.FromHours((double)-4.00); // UTC-4
DateTime newDateTime = utcDateTime.Add(offSet);
Console.WriteLine(newDateTime);
}
This is something i saw in a different post but it looks that it only changes the hour in a wrong way.. please help.

To get the current time in a particular offset (such as UTC-4), as a DateTime, the easiest way (IMHO) is:
DateTime dt = DateTimeOffset.UtcNow.ToOffset(TimeSpan.FromHours(-4)).DateTime;
Another (messier) way to get the same results would be:
DateTime dt = DateTime.SpecifyKind(DateTime.UtcNow.AddHours(-4), DateTimeKind.Unspecified);
One might also just keep it as a DateTimeOffset, such that the offset from UTC is not lost.
DateTimeOffset dto = DateTimeOffset.UtcNow.ToOffset(TimeSpan.FromHours(-4));
Or the messier way:
TimeSpan offset = TimeSpan.FromHours(-4);
DateTime dt = DateTime.SpecifyKind(DateTime.UtcNow.Add(offset), DateTimeKind.Unspecified);
DateTimeOffset dto = new DateTimeOffset(dt, offset);
However, in most cases, one is probably not working with a fixed offset, but is instead looking for the time in a particular time zone, which could be in a variety of different offsets depending on the date in question, due to both daylight saving time and changes in the standard time observed by a particular government.
See also "Time Zone != Offset" in the timezone tag wiki.
In .NET, the TimeZoneInfo class can manage such changes for you. On Windows, it uses Microsoft time zone identifiers, and on Linux or Mac OSX, it uses IANA time zone identifiers. For example:
// On Windows:
TimeZoneInfo tz = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");
DateTime dt = TimeZoneInfo.ConvertTime(DateTime.UtcNow, tz);
// On Linux/OSX:
TimeZoneInfo tz = TimeZoneInfo.FindSystemTimeZoneById("America/New_York");
DateTime dt = TimeZoneInfo.ConvertTime(DateTime.UtcNow, tz);
In both examples, the correct UTC offset (either UTC-5 for EST or UTC-4 for EDT) will be applied.
These could also be written using DateTimeOffset values:
// On Windows:
TimeZoneInfo tz = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");
DateTimeOffset dto = TimeZoneInfo.ConvertTime(DateTimeOffset.UtcNow, tz);
// On Linux/OSX:
TimeZoneInfo tz = TimeZoneInfo.FindSystemTimeZoneById("America/New_York");
DateTimeOffset dto = TimeZoneInfo.ConvertTime(DateTimeOffset.UtcNow, tz);
Additionally, if you need to write code that can run on either platform, you can use my TimeZoneConverter library to work with either set of identifiers on any platform.

Why all of you give so complex answers?
Is this wrong?
DateTime.UtcNow.AddHours(-4); //UTC-4

Format Local DateTime with appropriate Local DST-aware Timezone (eg. PST or PDT) depending on time of year

Given a Local DateTime value on a computer configured for PST (which will implicitly change to PDT on March 10th when DST kicks in), how can one obtain a string including the appropriate timezone - eg. PST/PDT, not offset! - in the output?
DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss ???")
Expected output strings, eg:
"2019-02-09 13:04:22 PST" // right after lunch today
"2019-04-09 13:04:22 PDT" // right after lunch in two months
The MSDN DateTime Custom Format Strings page shows examples of explicitly hard-coding "PST" into the output, which will be wrong half the year and/or when the local TZ is changed. Computers and people move, so hard-coding TZ values is simply 'not appropriate'.
Preferably this can be done with just a Format String, allowing DateTime values to be supplied until the rendering/to-string phase - although there does not appear to be a 'ZZZ' format. I've specified 'Local' DateTime Kind to, hopefully, reduce some additional quirks..

Since a DateTime instance does not keep timezone information, there is no way to do it with custom date and time format strings. "zzz" specifier is for UTC Offset value, DateTime.Kind with "K" specifier does not reflect time zone abbrevation neither. Both are useless for your case.
However, there is nuget package called TimeZoneNames which is written by time zone geek Matt Johnson that you can get abbreviations of a timezone name (supports both IANA and Windows time zone identifier)
var tz = TZNames.GetAbbreviationsForTimeZone("Pacific Standard Time", "en-US");
Console.WriteLine(tz.Standard); // PST
Console.WriteLine(tz.Daylight); // PDT
If you wanna get your windows time zone identifier programmatically, you can use TimeZoneInfo.Local.Id property, if you wanna get the current language code, you can use CultureInfo.CurrentCulture.Name property by the way.
var tz = TZNames.GetAbbreviationsForTimeZone(TimeZoneInfo.Local.Id, CultureInfo.CurrentCulture.Name);
But before that, you should check your local time is daylight saving time to choose which abbreviation to append your formatted string.
DateTime now = DateTime.Now;
bool isDaylight = TimeZoneInfo.Local.IsDaylightSavingTime(now);
If isDaylight is true, you should use the result of the TimeZoneValues.Daylight property, otherwise you should use TimeZoneValues.Standard property of the first code part.
At the end, you need append one of those abbreviation at the end of DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss) string.
For an important note from Matt on the package page;
Time zone abbreviations are sometimes inconsistent, and are not
necessarily localized correctly for every time zone. In most cases,
you should use abbreviations for end-user display output only. Do not
attempt to use abbreviations when parsing input.
Second important note from Matt's comment;
What makes you think that a time zone abbreviation actually exists for
every time zone and every language in the world? Even, then what makes
you think that a time zone abbreviation is enough to identify the time
zone? Hint - both questions are amorphous. Consider "CST" or "IST" -
Each have three or four places in the world that they might belong to.
Many many many other cases as well...

TimeZoneInfo should be able to help here: https://learn.microsoft.com/en-us/dotnet/api/system.timezoneinfo.standardname?view=netframework-4.7.2
It looks like TimeZoneInfo gives full names ("Pacific Standard Time"/"Pacific Daylight Time") rather than abbreviations ("PST"/"PDT"). It that's a problem, you'll still need to find a source for the short names. There are some ideas on how to do that here: Timezone Abbreviations
using System;
using Xunit;
namespace Q54610867
{
public class TimeZoneTests
{
// I'm on Mac/Unix. If you're on Windows, change the ID to "Pacific Standard Time"
// See: https://github.com/dotnet/corefx/issues/2538
readonly TimeZoneInfo pacificStandardTime = TimeZoneInfo.FindSystemTimeZoneById("America/Los_Angeles");
[Fact]
public void Today()
{
var today = new DateTime(2019, 2, 9, 13, 4, 22, DateTimeKind.Local);
Assert.Equal("2019-02-09 13:04:22 Pacific Standard Time", ToStringWithTz(today, pacificStandardTime));
}
[Fact]
public void future()
{
var future = new DateTime(2019, 4, 9, 13, 4, 22, DateTimeKind.Local);
Assert.Equal("2019-04-09 13:04:22 Pacific Daylight Time", ToStringWithTz(future, pacificStandardTime));
}
static string ToStringWithTz(DateTime dateTime, TimeZoneInfo tz)
=> $"{dateTime.ToString("yyyy-MM-dd HH:mm:ss")} {(tz.IsDaylightSavingTime(dateTime) ? tz.DaylightName : tz.StandardName)}";
}
}

How to convert string offset to timespan in c#

I'm trying to convert the convert time to the user's time zone, but I don't have the windows time zone string such as "Pacific Standard Time". All I have is a string offset such as "-07:00". Looks like I need to create a timespan. Is the only way to parse this string manually?. Seems like there should be a way to convert a time using a string offset, but maybe I am missing something.
I have this but it requires the timezone. I'm trying to modify it to use the offset instead, but you can see the timespan that is created for the conversion and I need to get my offset to the timespan.
static void Main(string[] args)
{
var currentTimeInPacificTime = ConvertUtcTimeToTimeZone(DateTime.UtcNow, "Pacific Standard Time");
//TimeSpan ts = new TimeSpan("-07:00");
Console.ReadKey();
}
static DateTimeOffset ConvertUtcTimeToTimeZone(DateTime dateTime, string toTimeZoneDesc)
{
if (dateTime.Kind != DateTimeKind.Utc) throw new Exception("dateTime needs to have Kind property set to Utc");
TimeSpan toUtcOffset = TimeZoneInfo.FindSystemTimeZoneById(toTimeZoneDesc).GetUtcOffset(dateTime);
var convertedTime = DateTime.SpecifyKind(dateTime.Add(toUtcOffset), DateTimeKind.Unspecified);
return new DateTimeOffset(convertedTime, toUtcOffset);
}

You can just use the TimeSpan.Parse method:
TimeSpan ts = TimeSpan.Parse("-07:00");
Console.WriteLine(ts); // -07:00:00
Be careful to strip a leading "+" as TimeSpan.Parse will fail here. "+01:00" is incorrect, but "01:00" works.
Or if you want be a little more safe, try the TimeSpan.TryParse method:
TimeSpan ts;
if (TimeSpan.TryParse("-07:00", out ts))
Console.WriteLine(ts); // -07:00:00
But of course if all you want to do is convert a UTC date/time to a local date/time, you can just do this:
DateTime localDateTime = utcDateTime.ToLocalTime();
Or to convert it to any timezone:
TimeZoneInfo tzi = TimeZoneInfo.FindSystemTimeZoneById(toTimeZoneDesc);
DateTime localDateTime = TimeZoneInfo.ConvertTime(utcDateTime, tzi);

For more complicated/non-standard formats you can also use TimeSpan.ParseExact(String, String, IFormatProvider), where the second String is a Custom TimeSpan Format String.
API information is available at msdn.microsoft.com, and is linked above.linked.

I'm trying to convert the convert time to the user's time zone, but I don't have the windows time zone string such as "Pacific Standard Time". All I have is a string offset such as "-07:00".
Then you don't have what you need to make the correct conversion. Read "Time Zone != Offset" in the timezone tag wiki.
It is important to understand that the "Pacific Standard Time" value is the .Id for the TimeZoneInfo object that is used for US Pacific Time. It covers both Pacific Standard Time (UTC-8) and Pacfic Daylight Time (UTC-7).
All I have is a string offset such as "-07:00". Looks like I need to create a timespan.
Now you have what is commonly called the XY Problem. You shouldn't have any need to work with the offset by itself.
In your code, there is a call to dateTime.Add(toUtcOffset). When doing time zone conversions, this is a code smell that you are doing it wrong. You should never have to manually add or subtract time just to manipulate time zones. That should be reserved for actually changing the moment in time you are talking about.
What you should be doing is to collect a real time zone id from your user. Either "Pacific Standard Time" for use with TimeZoneInfo, or "America/Los_Angeles" for use with a TZDB implementation like Noda Time.
If time zone conversions aren't important in your context, then you might just want to collect a full DateTimeOffset value such as 2013-08-17T13:27:00.000-07:00 instead.

There are time zone strings which includes "Pacific Standard Time". The complete list can be found here. http://www.xiirus.net/articles/article-_net-convert-datetime-from-one-timezone-to-another-7e44y.aspx
Any DateTime object can be converted to some timezone -
TimeZoneInfo timeZoneInfo;
DateTime dateTime ;
//Set the time zone information to Pacific Standard Time
timeZoneInfo = TimeZoneInfo.FindSystemTimeZoneById("Pacific Standard Time");
//Get date and time in US Mountain Standard Time
dateTime = TimeZoneInfo.ConvertTime(DateTime.Now, timeZoneInfo);
//Print out the date and time
Console.WriteLine(dateTime.ToString("yyyy-MM-dd HH-mm-ss"));
So you method can be modified as -
static DateTimeOffset ConvertUtcTimeToTimeZone(DateTime dateTime, string toTimeZoneDesc)
{
return new DateTimeOffset(TimeZoneInfo.ConvertTime(dateTime, TimeZoneInfo.FindSystemTimeZoneById(toTimeZoneDesc)));
}

.NET Get timezone offset by timezone name

In database I store all date/times in UTC.
I know user's timezone name ("US Eastern Standard Time" for example).
In order to display correct time I was thinking that I need to add user's timezone offset to UTC date/time. But how would I get timezone offset by timezone name?
Thank You!

You can use TimeZoneInfo.FindSystemTimeZoneById to get the TimeZoneInfo object using the supplied Id, then TimeZoneInfo.GetUtcOffset from that:
TimeZoneInfo tzi = TimeZoneInfo.FindSystemTimeZoneById("US Eastern Standard Time");
TimeSpan offset = tzi.GetUtcOffset( myDateTime);

You can use the TimeZoneInfo class's GetSystemTimeZones() method to fetch the list of all timezones configured on your server and match it to the one from your client.
Though why do you have timezones in the format "US Eastern Standard Time"? Where did that come from?

Rather than doing some manual addition you should take advantage of the ConvertTime method of TimeZoneInfo which will handle converting your date based on the TimeZone you specify.
var localizedDateTime = TimeZoneInfo.ConvertTime(yourDateTime, localTimeZoneInfo);