DateTime.FromFileTimeUtc() Method in C#

The DateTime.FromFileTimeUtc() method in C# converts a Windows file time to an equivalent UTC DateTime. This method is useful when working with file timestamps or system-level operations that use Windows file time format, which represents time as the number of 100-nanosecond intervals since January 1, 1601 UTC.

Syntax

Following is the syntax −

public static DateTime FromFileTimeUtc(long fileTime);

Parameters

The method accepts the following parameter −

• fileTime − A Windows file time expressed in ticks (100-nanosecond intervals since January 1, 1601 UTC).

Return Value

Returns a DateTime object that represents the UTC time equivalent to the specified Windows file time.

Using DateTime.FromFileTimeUtc() with Different Values

Example 1: Basic Usage

using System;

public class Demo {
   public static void Main() {
      DateTime d1 = DateTime.FromFileTimeUtc(6500000000000);
      Console.WriteLine("DateTime = {0:dd} {0:y}, {0:hh}:{0:mm}:{0:ss}", d1);
   }
}

The output of the above code is −

DateTime = 08 January 1601, 12:33:20

Example 2: Multiple File Time Conversions

using System;

public class Demo {
   public static void Main() {
      DateTime d1 = DateTime.FromFileTimeUtc(0);
      DateTime d2 = DateTime.FromFileTimeUtc(850000000000000);
      Console.WriteLine("DateTime = {0:dd} {0:y}, {0:hh}:{0:mm}:{0:ss}", d1);
      Console.WriteLine("New DateTime = {0:dd} {0:y}, {0:hh}:{0:mm}:{0:ss}", d2);
   }
}

The output of the above code is −

DateTime = 01 January 1601, 12:00:00
New DateTime = 11 September 1603, 07:06:40

Using DateTime.FromFileTimeUtc() with Current File Times

Example 3: Working with Current Time Values

using System;

public class Demo {
   public static void Main() {
      DateTime currentUtc = DateTime.UtcNow;
      long fileTime = currentUtc.ToFileTimeUtc();
      DateTime convertedBack = DateTime.FromFileTimeUtc(fileTime);
      
      Console.WriteLine("Original UTC: {0}", currentUtc.ToString("yyyy-MM-dd HH:mm:ss"));
      Console.WriteLine("File Time: {0}", fileTime);
      Console.WriteLine("Converted Back: {0}", convertedBack.ToString("yyyy-MM-dd HH:mm:ss"));
      Console.WriteLine("Are Equal: {0}", currentUtc.ToString("yyyy-MM-dd HH:mm:ss") == convertedBack.ToString("yyyy-MM-dd HH:mm:ss"));
   }
}

The output of the above code is −

Original UTC: 2023-10-15 14:30:45
File Time: 133421478450000000
Converted Back: 2023-10-15 14:30:45
Are Equal: True

Key Points

• Windows file time starts from January 1, 1601 UTC, not the Unix epoch (January 1, 1970).
• Each tick represents 100 nanoseconds (0.1 microseconds).
• The method always returns a UTC DateTime with Kind set to DateTimeKind.Utc.
• Use ToFileTimeUtc() to convert a DateTime back to Windows file time format.

Conclusion

The DateTime.FromFileTimeUtc() method provides an efficient way to convert Windows file time values to UTC DateTime objects. This is particularly useful when working with file system operations, system APIs, or when interfacing with Windows-based time representations that use the 100-nanosecond tick format starting from January 1, 1601 UTC.