How to use the DateOnly and TimeOnly structures

 How to use the DateOnly and TimeOnly structures

The DateOnly and TimeOnly structures were introduced with .NET 6 and represent a specific date or time-of-day, respectively. Prior to .NET 6, and always in .NET Framework, developers used the DateTime type (or some other alternative) to represent one of the following:

  • A whole date and time.
  • A date, disregarding the time.
  • A time, disregarding the date.

DateOnly and TimeOnly are types that represent those particular portions of a DateTime type.

 Important

DateOnly and TimeOnly types aren't available in .NET Framework.

The DateOnly structure

The DateOnly structure represents a specific date, without time. Since it has no time component, it represents a date from the start of the day to the end of the day. This structure is ideal for storing specific dates, such as a birth date, an anniversary date, or business-related dates.

Although you could use DateTime while ignoring the time component, there are a few benefits to using DateOnly over DateTime:

  • The DateTime structure may roll into the previous or next day if it's offset by a time zone. DateOnly can't be offset by a time zone, and it always represents the date that was set.

  • Serializing a DateTime structure includes the time component, which may obscure the intent of the data. Also, DateOnly serializes less data.

  • When code interacts with a database, such as SQL Server, whole dates are generally stored as the date data type, which doesn't include a time. DateOnly matches the database type better.

DateOnly has a range from 0001-01-01 through 9999-12-31, just like DateTime. You can specify a specific calendar in the DateOnly constructor. However, a DateOnly object always represents a date in the proleptic Gregorian calendar, regardless of which calendar was used to construct it. For example, you can build the date from a Hebrew calendar, but the date is converted to Gregorian:

var hebrewCalendar = new System.Globalization.HebrewCalendar();
var theDate = new DateOnly(5776, 2, 8, hebrewCalendar); // 8 Cheshvan 5776

Console.WriteLine(theDate);

/* This example produces the following output:
 *
 * 10/21/2015
*/

DateOnly examples

Use the following examples to learn about DateOnly:

Convert DateTime to DateOnly

Use the DateOnly.FromDateTime static method to create a DateOnly type from a DateTime type, as demonstrated in the following code:


var today = DateOnly.FromDateTime(DateTime.Now);
Console.WriteLine($"Today is {today}");

/* This example produces output similar to the following:
 * 
 * Today is 12/28/2022
*/

Add or subtract days, months, years

There are three methods used to adjust a DateOnly structure: AddDays, AddMonths, and AddYears. Each method takes an integer parameter, and increases the date by that measurement. If a negative number is provided, the date is decreased by that measurement. The methods return a new instance of DateOnly, as the structure is immutable.

var theDate = new DateOnly(2015, 10, 21);

var nextDay = theDate.AddDays(1);
var previousDay = theDate.AddDays(-1);
var decadeLater = theDate.AddYears(10);
var lastMonth = theDate.AddMonths(-1);

Console.WriteLine($"Date: {theDate}");
Console.WriteLine($" Next day: {nextDay}");
Console.WriteLine($" Previous day: {previousDay}");
Console.WriteLine($" Decade later: {decadeLater}");
Console.WriteLine($" Last month: {lastMonth}");

/* This example produces the following output:
 * 
 * Date: 10/21/2015
 *  Next day: 10/22/2015
 *  Previous day: 10/20/2015
 *  Decade later: 10/21/2025
 *  Last month: 9/21/2015
*/

Parse and format DateOnly

DateOnly can be parsed from a string, just like the DateTime structure. All of the standard .NET date-based parsing tokens work with DateOnly. When converting a DateOnly type to a string, you can use standard .NET date-based formatting patterns too. For more information about formatting strings, see Standard date and time format strings.

var theDate = DateOnly.ParseExact("21 Oct 2015", "dd MMM yyyy", CultureInfo.InvariantCulture);  // Custom format
var theDate2 = DateOnly.Parse("October 21, 2015", CultureInfo.InvariantCulture);

Console.WriteLine(theDate.ToString("m", CultureInfo.InvariantCulture));     // Month day pattern
Console.WriteLine(theDate2.ToString("o", CultureInfo.InvariantCulture));    // ISO 8601 format
Console.WriteLine(theDate2.ToLongDateString());

/* This example produces the following output:
 * 
 * October 21
 * 2015-10-21
 * Wednesday, October 21, 2015
*/

Compare DateOnly

DateOnly can be compared with other instances. For example, you can check if a date is before or after another, or if a date today matches a specific date.

var theDate = DateOnly.ParseExact("21 Oct 2015", "dd MMM yyyy", CultureInfo.InvariantCulture);  // Custom format
var theDate2 = DateOnly.Parse("October 21, 2015", CultureInfo.InvariantCulture);
var dateLater = theDate.AddMonths(6);
var dateBefore = theDate.AddDays(-10);

Console.WriteLine($"Consider {theDate}...");
Console.WriteLine($" Is '{nameof(theDate2)}' equal? {theDate == theDate2}");
Console.WriteLine($" Is {dateLater} after? {dateLater > theDate} ");
Console.WriteLine($" Is {dateLater} before? {dateLater < theDate} ");
Console.WriteLine($" Is {dateBefore} after? {dateBefore > theDate} ");
Console.WriteLine($" Is {dateBefore} before? {dateBefore < theDate} ");

/* This example produces the following output:
 * 
 * Consider 10/21/2015
 *  Is 'theDate2' equal? True
 *  Is 4/21/2016 after? True
 *  Is 4/21/2016 before? False
 *  Is 10/11/2015 after? False
 *  Is 10/11/2015 before? True
*/

The TimeOnly structure

The TimeOnly structure represents a time-of-day value, such as a daily alarm clock or what time you eat lunch each day. TimeOnly is limited to the range of 00:00:00.0000000 - 23:59:59.9999999, a specific time of day.

Prior to the TimeOnly type being introduced, programmers typically used either the DateTime type or the TimeSpan type to represent a specific time. However, using these structures to simulate a time without a date may introduce some problems, which TimeOnly solves:

  • TimeSpan represents elapsed time, such as time measured with a stopwatch. The upper range is more than 29,000 years, and its value can be negative to indicate moving backwards in time. A negative TimeSpan doesn't indicate a specific time of the day.

  • If TimeSpan is used as a time of day, there's a risk that it could be manipulated to a value outside of the 24-hour day. TimeOnly doesn't have this risk. For example, if an employee's work shift starts at 18:00 and lasts for 8 hours, adding 8 hours to the TimeOnly structure rolls over to 2:00

  • Using DateTime for a time of day requires that an arbitrary date be associated with the time, and then later disregarded. It's common practice to choose DateTime.MinValue (0001-01-01) as the date, however, if hours are subtracted from the DateTime value, an OutOfRange exception might occur. TimeOnly doesn't have this problem as the time rolls forwards and backwards around the 24-hour timeframe.

  • Serializing a DateTime structure includes the date component, which may obscure the intent of the data. Also, TimeOnly serializes less data.

TimeOnly examples

Use the following examples to learn about TimeOnly:

Convert DateTime to TimeOnly

Use the TimeOnly.FromDateTime static method to create a TimeOnly type from a DateTime type, as demonstrated in the following code:

var now = TimeOnly.FromDateTime(DateTime.Now);
Console.WriteLine($"It is {now} right now");

/* This example produces output similar to the following:
 * 
 * It is 2:01 PM right now
*/

Add or subtract time

There are three methods used to adjust a TimeOnly structure: AddHours, AddMinutes, and Add. Both AddHours and AddMinutes take an integer parameter, and adjust the value accordingly. You can use a negative value to subtract and a positive value to add. The methods return a new instance of TimeOnly is returned, as the structure is immutable. The Add method takes a TimeSpan parameter and adds or subtracts the value from the TimeOnly value.

Because TimeOnly only represents a 24-hour period, it rolls over forwards or backwards appropriately when adding values supplied to those three methods. For example, if you use a value of 01:30:00 to represent 1:30 AM, then add -4 hours from that period, it rolls backwards to 21:30:00, which is 9:30 PM. There are method overloads for AddHours, AddMinutes, and Add that capture the number of days rolled over.

var theTime = new TimeOnly(7, 23, 11);

var hourLater = theTime.AddHours(1);
var minutesBefore = theTime.AddMinutes(-12);
var secondsAfter = theTime.Add(TimeSpan.FromSeconds(10));
var daysLater = theTime.Add(new TimeSpan(hours: 21, minutes: 200, seconds: 83), out int wrappedDays);
var daysBehind = theTime.AddHours(-222, out int wrappedDaysFromHours);

Console.WriteLine($"Time: {theTime}");
Console.WriteLine($" Hours later: {hourLater}");
Console.WriteLine($" Minutes before: {minutesBefore}");
Console.WriteLine($" Seconds after: {secondsAfter}");
Console.WriteLine($" {daysLater} is the time, which is {wrappedDays} days later");
Console.WriteLine($" {daysBehind} is the time, which is {wrappedDaysFromHours} days prior");

/* This example produces the following output:
 * 
 * Time: 7:23 AM
 *  Hours later: 8:23 AM
 *  Minutes before: 7:11 AM
 *  Seconds after: 7:23 AM
 *  7:44 AM is the time, which is 1 days later 
 *  1:23 AM is the time, which is -9 days prior
*/

Parse and format TimeOnly

TimeOnly can be parsed from a string, just like the DateTime structure. All of the standard .NET time-based parsing tokens work with TimeOnly. When converting a TimeOnly type to a string, you can use standard .NET date-based formatting patterns too. For more information about formatting strings, see Standard date and time format strings.

var theTime = TimeOnly.ParseExact("5:00 pm", "h:mm tt", CultureInfo.InvariantCulture);  // Custom format
var theTime2 = TimeOnly.Parse("17:30:25", CultureInfo.InvariantCulture);

Console.WriteLine(theTime.ToString("o", CultureInfo.InvariantCulture));     // Round-trip pattern.
Console.WriteLine(theTime2.ToString("t", CultureInfo.InvariantCulture));    // Long time format
Console.WriteLine(theTime2.ToLongTimeString());

/* This example produces the following output:
 * 
 * 17:00:00.0000000
 * 17:30
 * 5:30:25 PM
*/

Serialize DateOnly and TimeOnly types

With .NET 7+, System.Text.Json supports serializing and deserializing DateOnly and TimeOnly types. Consider the following object:

sealed file record Appointment(
    Guid Id,
    string Description,
    DateOnly Date,
    TimeOnly StartTime,
    TimeOnly EndTime);

The following example serializes an Appointment object, displays the resulting JSON, and then deserializes it back into a new instance of the Appointment type. Finally, the original and newly deserialized instances are compared for equality and the results are written to the console:

Appointment originalAppointment = new(
    Id: Guid.NewGuid(),
    Description: "Take dog to veterinarian.",
    Date: new DateOnly(2002, 1, 13),
    StartTime: new TimeOnly(5,15),
    EndTime: new TimeOnly(5, 45));
string serialized = JsonSerializer.Serialize(originalAppointment);

Console.WriteLine($"Resulting JSON: {serialized}");

Appointment deserializedAppointment =
    JsonSerializer.Deserialize<Appointment>(serialized)!;

bool valuesAreTheSame = originalAppointment == deserializedAppointment;
Console.WriteLine($"""
    Original record has the same values as the deserialized record: {valuesAreTheSame}
    """);

In the preceding code:

  • An Appointment object is instantiated and assigned to the appointment variable.
  • The appointment instance is serialized to JSON using JsonSerializer.Serialize.
  • The resulting JSON is written to the console.
  • The JSON is deserialized back into a new instance of the Appointment type using JsonSerializer.Deserialize.
  • The original and newly deserialized instances are compared for equality.
  • The result of the comparison is written to the console.

For more information, see How to serialize and deserialize JSON in .NET.

Work with TimeSpan and DateTime

TimeOnly can be created from and converted to a TimeSpan. Also, TimeOnly can be used with a DateTime, either to create the TimeOnly instance, or to create a DateTime instance as long as a date is provided.

The following example creates a TimeOnly object from a TimeSpan, and then converts it back:

// TimeSpan must in the range of 00:00:00.0000000 to 23:59:59.9999999
var theTime = TimeOnly.FromTimeSpan(new TimeSpan(23, 59, 59));
var theTimeSpan = theTime.ToTimeSpan();

Console.WriteLine($"Variable '{nameof(theTime)}' is {theTime}");
Console.WriteLine($"Variable '{nameof(theTimeSpan)}' is {theTimeSpan}");

/* This example produces the following output:
 * 
 * Variable 'theTime' is 11:59 PM
 * Variable 'theTimeSpan' is 23:59:59
*/

The following example creates a DateTime from a TimeOnly object, with an arbitrary date chosen:

var theTime = new TimeOnly(11, 25, 46);   // 11:25 AM and 46 seconds
var theDate = new DateOnly(2015, 10, 21); // October 21, 2015
var theDateTime = theDate.ToDateTime(theTime);
var reverseTime = TimeOnly.FromDateTime(theDateTime);

Console.WriteLine($"Date only is {theDate}");
Console.WriteLine($"Time only is {theTime}");
Console.WriteLine();
Console.WriteLine($"Combined to a DateTime type, the value is {theDateTime}");
Console.WriteLine($"Converted back from DateTime, the time is {reverseTime}");

/* This example produces the following output:
 * 
 * Date only is 10/21/2015
 * Time only is 11:25 AM
 * 
 * Combined to a DateTime type, the value is 10/21/2015 11:25:46 AM
 * Converted back from DateTime, the time is 11:25 AM
*/

Arithmetic operators and comparing TimeOnly

Two TimeOnly instances can be compared with one another, and you can use the IsBetween method to check if a time is between two other times. When an addition or subtraction operator is used on a TimeOnly, a TimeSpan is returned, representing a duration of time.

var start = new TimeOnly(10, 12, 01); // 10:12:01 AM
var end = new TimeOnly(14, 00, 53); // 02:00:53 PM

var outside = start.AddMinutes(-3);
var inside = start.AddMinutes(120);

Console.WriteLine($"Time starts at {start} and ends at {end}");
Console.WriteLine($" Is {outside} between the start and end? {outside.IsBetween(start, end)}");
Console.WriteLine($" Is {inside} between the start and end? {inside.IsBetween(start, end)}");
Console.WriteLine($" Is {start} less than {end}? {start < end}");
Console.WriteLine($" Is {start} greater than {end}? {start > end}");
Console.WriteLine($" Does {start} equal {end}? {start == end}");
Console.WriteLine($" The time between {start} and {end} is {end - start}");

/* This example produces the following output:
 * 
 * Time starts at 10:12 AM and ends at 2:00 PM
 *  Is 10:09 AM between the start and end? False
 *  Is 12:12 PM between the start and end? True
 *  Is 10:12 AM less than 2:00 PM? True
 *  Is 10:12 AM greater than 2:00 PM? False
 *  Does 10:12 AM equal 2:00 PM? False
 *  The time between 10:12 AM and 2:00 PM is 03:48:52
*/

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