The DateTime value type represents dates and times with values ranging from 00:00:00 (midnight), January 1, 0001 Anno Domini (Common Era) through 11:59:59 P.M., December 31, 9999 A.D. (C.E.) in the Gregorian calendar.

Time values are measured in 100-nanosecond units called ticks, and a particular date is the number of ticks since 12:00 midnight, January 1, 0001 A.D. (C.E.) in the GregorianCalendar calendar (excluding ticks that would be added by leap seconds). For example, a ticks value of 31241376000000000L represents the date, Friday, January 01, 0100 12:00:00 midnight. A DateTime value is always expressed in the context of an explicit or default calendar.

Starting with the .NET Framework 2.0, the DateTime structure contains a 64-bit field composed of a private Kind field concatenated with the Ticks field. The Kind field is a 2-bit field that indicates whether the DateTime structure represents a local time, a Coordinated Universal Time (UTC), or the time in an unspecified time zone. The Kind field is used when performing time conversions between time zones, but not for time comparisons or arithmetic. The value of the Kind field can be obtained with the Kind property.

IEEE 64 ビット (8 バイト) の整数として格納され、西暦 0001 年 1 月 1 日から西暦 9999 年 12 月 31 日までの日付と、午前 12:00:00 から午後 11:59:59.9999999 までの時刻を表します。 増分は、グレゴリオ暦の西暦 1 年 1 月 1 日からの経過時間の 100 ナノ秒を表します。 最大値は、西暦 10000 年 1 月 1 日の 100 ナノ秒前です。