How to get current user TimeZone in C#

You will need to use both client-side and server-side technologies.

On the client side:
(pick one)

• This works in most modern browsers:

  Intl.DateTimeFormat().resolvedOptions().timeZone
  

• There is also jsTimeZoneDetect's jstz.determine(), or Moment-Timezone's moment.tz.guess() function for older browsers.

The result from either will be an IANA time zone identifier, such as America/Los_Angeles. Send that result to the server by any means you like.

On the server side:
(pick one)

• Using TimeZoneInfo (on Non-Windows systems only):

  TimeZoneInfo tzi = TimeZoneInfo.FindSystemTimeZoneById("America/New_York");
  

• Using TimeZoneConverter (on any OS):

  TimeZoneInfo tzi = TZConvert.GetTimeZoneInfo("America/New_York");
  

• Using NodaTime (on any OS):

  DateTimeZone tz = DateTimeZoneProviders.Tzdb["America/New_York"];