Correct approach to getting the universal time zone

Question

In my project I want to get the universal time zone. I used two different kinds of approaches but I don't know which one is the best practice.

First approach is

public static DateTime GetUniversalTime(DateTime localDateTime)
{
    TimeZone zone = TimeZone.CurrentTimeZone;
    DateTime universal = zone.ToUniversalTime(localDateTime);
    return universal;
}

then I want revert to local time I used the below method:

public static DateTime GetLocalTime(DateTime universalDateTime)
{
    TimeZone zone = TimeZone.CurrentTimeZone;
    DateTime local = zone.ToLocalTime(universalDateTime);
    return local;
}

and second approach is get universal time zone DateTime.UtcNow; then I want to revert to local time I used the above GetLocalTime method.

Can one explain what is the different between the above two approaches?

Which one is the best practice ?

Answer 1

Since you are asking about best practices:

• Do not use the TimeZone class. If you need time zone conversions, use the TimeZoneInfo class instead. This is very clear in the MSDN documentation:

  

• Whenever possible, avoid any use of "local" time. It is local to the system where the code is running. In the vast majority of real-world use cases, it is likely that it is not the local time zone of your user. This is especially true in a web application.

  That means you should not be calling any of the following:

  • DateTime.Now
  • TimeZone.CurrentTimeZone
  • TimeZoneInfo.Local
  • DateTime.ToLocalTime()
  • DateTime.ToUniversalTime()
  • Any other method that involves the server's local time zone.
    
    

• Instead, your application should allow the user to select a time zone, then you can convert to and from the local time in that zone using the TimeZoneInfo.Convert... methods.

• If you need the current universal time, use DateTime.UtcNow or DateTimeOffset.UtcNow.

• If you need the current local time zone of your server, ONLY use DateTimeOffset.Now.

• If you need the current local time in a known time zone, such as US Eastern Time:

  DateTime easternNow = TimeZoneInfo.ConvertTimeBySystemTimeZoneId(
                                     DateTime.UtcNow, "Eastern Standard Time");
  

• If you want to convert between a known time zone and UTC, then use the TimeZoneInfo.ConvertTimeToUtc and TimeZoneInfo.ConvertTimeFromUtc methods, and be sure to pass in the time zone you are converting to/from:

  // get the local time zone of your user, not of the server!
  TimeZoneInfo tzi = TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time");
  
  // use this to convert from UTC to local
  DateTime local = TimeZoneInfo.ConvertTimeFromUtc(yourUtcDateTime, tzi);
  
  // use this to convert from local to UTC
  DateTime utc = TimeZoneInfo.ConvertTimeToUtc(yourLocalDateTime, tzi);
  

  Be aware that when you convert from local to UTC, you might encounter ambiguities during daylight saving time transitions. Read more in the DST tag wiki.

Additional reading: The Case Against DateTime.Now

Answer 2

For Universal Time.

DateTime.Now.ToUniversalTime()

For Local Time

DateTime.UtcNow.ToLocalTime()

Universal To Local

var nowUtc = DateTime.Now.ToUniversalTime();
var nowLocal = nowUtc.ToLocalTime();