DateTime.Now / DateTime.Today

DateTime dt = DateTime.Now;

// Gets today's date (time is 00:00:00).
DateTime dt = DateTime.Today;

DateTime dt = DateTime.UtcNow;

Program.cs

using System;

DateTime now = DateTime.Now;
Console.WriteLine(now); // e.g., 1/15/2024 2:30:45 PM

// Gets today's date (no time component).
DateTime today = DateTime.Today;
Console.WriteLine(today); // e.g., 1/15/2024 12:00:00 AM

// Gets each component individually.
Console.WriteLine($"Year: {now.Year}");
Console.WriteLine($"Month: {now.Month}");
Console.WriteLine($"Day: {now.Day}");
Console.WriteLine($"Hour: {now.Hour}");
Console.WriteLine($"Minute: {now.Minute}");
Console.WriteLine($"Second: {now.Second}");

Console.WriteLine($"Day of week: {now.DayOfWeek}");

// Displays the day of the week as a short name.
string[] dayNames = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };
Console.WriteLine($"Day of week (short): {dayNames[(int)now.DayOfWeek]}");

DateTime utc = DateTime.UtcNow;
Console.WriteLine($"UTC: {utc}");

Run the following command:

dotnet script datetime_now_today.csx
1/15/2024 2:30:45 PM
1/15/2024 12:00:00 AM
Year: 2024
Month: 1
Day: 15
Hour: 14
Minute: 30
Second: 45
Day of week: Monday
Day of week (short): Mon
UTC: 1/15/2024 5:30:45 AM

DateTime values can be compared directly using comparison operators (<, >, ==). This is useful for birthday checks and expiration date validation.

DateComparison.cs

using System;

// Birthday: Rintaro Okabe (born December 14, 2000, for this example)
DateTime birthday = new DateTime(2000, 12, 14);
DateTime today = DateTime.Today;

bool isBirthday = today.Month == birthday.Month && today.Day == birthday.Day;
Console.WriteLine($"Today is a birthday: {isBirthday}");

// Calculates age.
int age = today.Year - birthday.Year;
if (today < birthday.AddYears(age))
    age--;
Console.WriteLine($"Age: {age}");

// Expiration check (is the expiry date before today?).
DateTime expiry = new DateTime(2024, 3, 31);
bool isExpired = expiry < today;
Console.WriteLine($"Expired: {isExpired}");

// Uses MinValue as a sentinel for "not set".
DateTime lastLogin = DateTime.MinValue;
if (lastLogin == DateTime.MinValue)
    Console.WriteLine("Never logged in.");

Run the following command:

dotnet script date_comparison.csx
Today is a birthday: False
Age: 23
Expired: True
Never logged in.

On the server side, the standard practice is to store dates in UTC and convert to local time only for display.

TimeZoneExample.cs

using System;

// Use UtcNow for logging and database storage.
DateTime utcNow = DateTime.UtcNow;
Console.WriteLine($"UTC (for storage): {utcNow:yyyy-MM-dd HH:mm:ss}");

// Convert to JST (UTC+9) for display.
TimeZoneInfo jst = TimeZoneInfo.FindSystemTimeZoneById("Tokyo Standard Time");
DateTime jstNow = TimeZoneInfo.ConvertTimeFromUtc(utcNow, jst);
Console.WriteLine($"JST (for display): {jstNow:yyyy-MM-dd HH:mm:ss}");

// DateTimeOffset includes time zone offset information.
DateTimeOffset now = DateTimeOffset.UtcNow;
DateTimeOffset jstOffset = now.ToOffset(TimeSpan.FromHours(9));
Console.WriteLine($"DateTimeOffset JST: {jstOffset:yyyy-MM-dd HH:mm:ss zzz}");

Run the following command:

dotnet script timezone_example.csx
UTC (for storage): 2024-01-15 05:30:45
JST (for display): 2024-01-15 14:30:45
DateTimeOffset JST: 2024-01-15 14:30:45 +09:00

Common Mistake 1: Calling DateTime.Now Multiple Times

DateTime.Now retrieves the current time each time it is called. Calling it multiple times introduces slight time differences between values, so store it in a variable first.

using System;

// NG: Calling it twice means "start" and "done" have slightly different times.
Console.WriteLine($"Start: {DateTime.Now}");
// ...some processing...
Console.WriteLine($"Done: {DateTime.Now}");

// OK: Store the value in a variable and reuse it.
DateTime start = DateTime.Now;
Console.WriteLine($"Start: {start}");
// ...some processing...
Console.WriteLine($"Done: {start}"); // Displays the same time.

Common Mistake 2: Confusing DateTime.Today with DateTime.Now

When comparing by date only, using DateTime.Now includes the time component, which can cause "same day" comparisons to fail.

using System;

DateTime targetDate = new DateTime(2024, 1, 15); // No time component

// NG: DateTime.Now includes a time component, so == comparison fails unless the time is exactly 00:00:00.
bool wrong = DateTime.Now == targetDate;

// OK: Use DateTime.Today for date-only comparison.
bool correct = DateTime.Today == targetDate;
Console.WriteLine($"Today: {correct}");

// Alternatively, strip the time using the .Date property.
bool alsoCorrect = DateTime.Now.Date == targetDate;
Console.WriteLine($"Now.Date: {alsoCorrect}");

Both DateTime.Now and DateTime.Today are static properties. Since they retrieve the current time each time they are called, store the value in a variable if you need to use it multiple times within the same operation.

For logging and database storage, use DateTime.UtcNow, which is not affected by time zone differences. To format a date and time as a string, see DateTime.ToString() / DateTime.AddDays().