The Korean calendar works exactly like the Gregorian calendar, except that the year and era are different.
The KoreanCalendar class recognizes only the current era.
Leap years in the Korean calendar correspond to the same leap years in the Gregorian calendar. A leap year in the Gregorian calendar is defined as a Gregorian year that is evenly divisible by four, except if it is divisible by 100; however, Gregorian years that are divisible by 400 are leap years. A common year has 365 days and a leap year has 366 days.
The Korean calendar has 12 months with 28 to 31 days each:
| GetMonth value | Month | Days in common years | Days in leap years |
| 1 | 1월 (January) | 31 | 31 |
| 2 | 2월 (February) | 28 | 29 |
| 3 | 3월 (March) | 31 | 31 |
| 4 | 4월 (April) | 30 | 30 |
| 5 | 5월 (May) | 31 | 31 |
| 6 | 6월 (June) | 30 | 30 |
| 7 | 7월 (July) | 31 | 31 |
| 8 | 8월 (August) | 31 | 31 |
| 9 | 9월 (September) | 30 | 30 |
| 10 | 10월 (October) | 31 | 31 |
| 11 | 11월 (November) | 30 | 30 |
| 12 | 12월 (December) | 31 | 31 |
February has 29 days during leap years and 28 during common years.
The date January 1, 2001 A.D. in the Gregorian calendar is equivalent to the first day of January in the year 4334 of the current era in the Korean calendar.
Each CultureInfo supports a set of calendars. The Calendar property returns the default calendar for the culture, and the OptionalCalendars property returns an array containing all the calendars supported by the culture. To change the calendar used by a CultureInfo, set the Calendar property of CultureInfo.DateTimeFormat to a new Calendar.