DateTime & TimeSpan Operations in C#

In C#, the DateTime and TimeSpan structures are used for working with dates and times. DateTime represents a specific moment, while TimeSpan represents the difference between two dates, i.e., a time interval. With these structures, operations such as comparing dates, adding/subtracting time, and formatting can easily be performed.

What is DateTime?

The DateTime structure represents a specific date and time.

DateTime now = DateTime.Now;
Console.WriteLine(now);           // Current date and time
Console.WriteLine(DateTime.UtcNow); // Universal time

Basic Properties of DateTime

You can extract individual date and time components:

DateTime date = new DateTime(2025, 9, 9, 14, 30, 0);

Console.WriteLine(date.Year);   // 2025
Console.WriteLine(date.Month);  // 9
Console.WriteLine(date.Day);    // 9
Console.WriteLine(date.Hour);   // 14
Console.WriteLine(date.Minute); // 30

Console.WriteLine(date.ToShortDateString()); // 9/9/2025
Console.WriteLine(date.ToLongDateString());  // Tuesday, September 9, 2025

Working with DateTime

Use Add methods to add or subtract days, months, or years.

DateTime today = DateTime.Now;

Console.WriteLine(today.AddDays(5));    // 5 days later
Console.WriteLine(today.AddMonths(-1)); // 1 month earlier

DateTime future = today.AddYears(1);
Console.WriteLine(future); // 1 year later

// Difference between two dates
DateTime birth = new DateTime(2000, 1, 1);
TimeSpan diff = today - birth;

Console.WriteLine($"Total days: {diff.Days}");

What is TimeSpan?

TimeSpan represents a time interval.

TimeSpan duration = new TimeSpan(2, 30, 0); // 2 hours 30 minutes
Console.WriteLine(duration.TotalMinutes);   // 150 minutes

Using DateTime with TimeSpan

You can add a TimeSpan to a DateTime to create a new date.

DateTime now = DateTime.Now;
TimeSpan threeHours = new TimeSpan(3, 0, 0);

DateTime newDate = now + threeHours;
Console.WriteLine(newDate);

Comparing Dates

Dates can be compared using >, <, ==, or the Compare method.

DateTime d1 = new DateTime(2025, 1, 1);
DateTime d2 = new DateTime(2025, 12, 31);

Console.WriteLine(d1 < d2); // true
Console.WriteLine(DateTime.Compare(d1, d2)); // -1 (d1 is earlier)

Checking whether a date is in a specific year or month:

DateTime date = new DateTime(2025, 9, 9);

bool sameYear = (date.Year == 2025);  // true
bool sameMonth = (date.Month == 9);   // true

Date Formatting

With the ToString method, you can apply custom formats.

DateTime now = DateTime.Now;

Console.WriteLine(now.ToString("dd.MM.yyyy"));       // 09.09.2025
Console.WriteLine(now.ToString("dd.MM.yy"));         // 09.09.25
Console.WriteLine(now.ToString("yyyy-MM-dd HH:mm")); // 2025-09-09 14:45

Sample Application: Project Duration and Daily Rate Calculation

Console.Write("Enter project start date (yyyy-MM-dd): ");
DateTime start = DateTime.Parse(Console.ReadLine());

Console.Write("Enter project end date (yyyy-MM-dd): ");
DateTime end = DateTime.Parse(Console.ReadLine());

if (end <= start)
{
    Console.WriteLine("Error: End date must be after the start date.");
}
else
{
    Console.Write("Enter total project price: ");
    decimal price = decimal.Parse(Console.ReadLine());

    TimeSpan duration = end - start;
    int days = duration.Days;

    decimal dailyRate = price / days;

    Console.WriteLine($"Project duration: {days} days");
    Console.WriteLine($"Daily rate: {dailyRate:0.00} USD");
}

TL;DR