Convert UTC/GMT time to local time

TimeZone.CurrentTimeZone.ToLocalTime(date);

I know this is an older question, but I ran into a similar situation, and I wanted to share what I had found for future searchers, possibly including myself :).

DateTime.Parse() can be tricky -- see here for example.

If the DateTime is coming from a Web service or some other source with a known format, you might want to consider something like

DateTime.ParseExact(dateString, 
                   "MM/dd/yyyy HH:mm:ss", 
                   CultureInfo.InvariantCulture, 
                   DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal)

or, even better,

DateTime.TryParseExact(...)

The AssumeUniversal flag tells the parser that the date/time is already UTC; the combination of AssumeUniversal and AdjustToUniversal tells it not to convert the result to "local" time, which it will try to do by default. (I personally try to deal exclusively with UTC in the business / application / service layer(s) anyway. But bypassing the conversion to local time also speeds things up -- by 50% or more in my tests, see below.)

Here's what we were doing before:

DateTime.Parse(dateString, new CultureInfo("en-US"))

We had profiled the app and found that the DateTime.Parse represented a significant percentage of CPU usage. (Incidentally, the CultureInfo constructor was not a significant contributor to CPU usage.)

So I set up a console app to parse a date/time string 10000 times in a variety of ways. Bottom line:
Parse() 10 sec
ParseExact() (converting to local) 20-45 ms
ParseExact() (not converting to local) 10-15 ms
... and yes, the results for Parse() are in seconds,

Don't forget if you already have a DateTime object and are not sure if it's UTC or Local, it's easy enough to use the methods on the object directly:

DateTime convertedDate = DateTime.Parse(date);
DateTime localDate = convertedDate.ToLocalTime();

How do we adjust for the extra hour?

Unless specified .net will use the local pc settings. I'd have a read of: http://msdn.microsoft.com/en-us/library/system.globalization.daylighttime.aspx

By the looks the code might look something like:

DaylightTime daylight = TimeZone.CurrentTimeZone.GetDaylightChanges( year );

And as mentioned above double check what timezone setting your server is on. There are articles on the net for how to safely affect the changes in IIS.

In answer to Dana's suggestion:

The code sample now looks like:

string date = "Web service date"..ToString("R", ci);
DateTime convertedDate = DateTime.Parse(date);            
DateTime dt = TimeZone.CurrentTimeZone.ToLocalTime(convertedDate);

The original date was 20/08/08; the kind was UTC.

Both "convertedDate" and "dt" are the same:

21/08/08 10:00:26; the kind was local