TimeSpan / Date Difference Calculation

// Subtract two DateTime values to get the difference.
TimeSpan diff = dateTime2 - dateTime1;

// Create a TimeSpan directly.
TimeSpan ts = new TimeSpan(int hours, int minutes, int seconds);
TimeSpan ts = new TimeSpan(int days, int hours, int minutes, int seconds);

// Create a TimeSpan using static methods.
TimeSpan ts = TimeSpan.FromDays(double value);
TimeSpan ts = TimeSpan.FromHours(double value);
TimeSpan ts = TimeSpan.FromMinutes(double value);

using System;

// Calculate the difference between two DateTime values.
DateTime start = new DateTime(2024, 1, 1, 9, 0, 0);
DateTime end   = new DateTime(2024, 1, 3, 17, 30, 0);

TimeSpan diff = end - start;
Console.WriteLine($"Days: {diff.Days}");              // 2
Console.WriteLine($"Hours: {diff.Hours}");            // 8
Console.WriteLine($"Minutes: {diff.Minutes}");        // 30
Console.WriteLine($"Total hours: {diff.TotalHours}"); // 56.5
Console.WriteLine($"Total minutes: {diff.TotalMinutes}"); // 3390

// Measure elapsed time for a piece of code.
DateTime measureStart = DateTime.Now;
// ...some processing...
System.Threading.Thread.Sleep(100); // Wait 100 ms (for demonstration)
TimeSpan elapsed = DateTime.Now - measureStart;
Console.WriteLine($"Elapsed: {elapsed.TotalMilliseconds:F0} ms");

// Create a TimeSpan directly.
TimeSpan workTime = new TimeSpan(8, 30, 0); // 8 hours 30 minutes
Console.WriteLine($"Work time: {workTime.TotalHours} hours");

// Calculate the number of days until a deadline.
DateTime deadline = new DateTime(2024, 12, 31);
TimeSpan remaining = deadline - DateTime.Today;
Console.WriteLine($"Days until deadline: {(int)remaining.TotalDays}");

TimeSpan is a type that represents a length of time. .Days returns only the days component of the interval, whereas .TotalDays returns the entire interval converted to days as a decimal value. Use whichever property suits your needs.

For measuring code execution time, the System.Diagnostics.Stopwatch class is a better fit. Start it with Stopwatch.StartNew() and read the elapsed time via stopwatch.Elapsed.

For formatting and adding to date/time values, see DateTime.ToString() / DateTime.AddDays().