DAY

Returns the day of a date, represented by a serial number. The day is given as an integer ranging from 1 to 31.
Syntax
DAY(serial_number)
Serial_number    is the date of the day you are trying to find. Dates should be entered by using the DATE function, or as results of other formulas or functions. For example, use DATE(2008,5,23) for the 23rd day of May, 2008. Problems can occur if dates are entered as text.
Remarks
Microsoft Excel stores dates as sequential serial numbers so they can be used in calculations. By default, January 1, 1900 is serial number 1, and January 1, 2008 is serial number 39448 because it is 39,448 days after January 1, 1900. Microsoft Excel for the Macintosh uses a different date system as its default.
Values returned by the YEAR, MONTH and DAY functions will be Gregorian values regardless of the display format for the supplied date value. For example, if the display format of the supplied date is Hijri, the returned values for the YEAR, MONTH and DAY functions will be values associated with the equivalent Gregorian date.
Example
The example may be easier to understand if you copy it to a blank worksheet.

	A
1	Date
2	15-Apr-2008

Formula	Description (Result)
=DAY(A2)	Day of the date above (15)

DATE

Returns the sequential serial number that represents a particular date. If the cell format was General before the function was entered, the result is formatted as a date.
Syntax
DATE(year,month,day)
Year    The year argument can be one to four digits. Microsoft Excel interprets the year argument according to the date system you are using. By default, Excel for Windows uses the 1900 date system; Excel for the Macintosh uses the 1904 date system.

For the 1900 date system

·         If year is between 0 (zero) and 1899 (inclusive), Excel adds that value to 1900 to calculate the year. For example, DATE(108,1,2) returns January 2, 2008 (1900+108).

·         If year is between 1900 and 9999 (inclusive), Excel uses that value as the year. For example, DATE(2008,1,2) returns January 2, 2008.

·         If year is less than 0 or is 10000 or greater, Excel returns the #NUM! error value.

For the 1904 date system

·         If year is between 4 and 1899 (inclusive), Excel adds that value to 1900 to calculate the year. For example, DATE(108,1,2) returns January 2, 2008 (1900+108).

·         If year is between 1904 and 9999 (inclusive), Excel uses that value as the year. For example, DATE(2008,1,2) returns January 2, 2008.

·         If year is less than 4 or is 10000 or greater or if year is between 1900 and 1903 (inclusive), Excel returns the #NUM! error value.

Month    is a number representing the month of the year. If month is greater than 12, month adds that number of months to the first month in the year specified. For example, DATE(2008,14,2) returns the serial number representing February 2, 2009.
Day    is a number representing the day of the month. If day is greater than the number of days in the month specified, day adds that number of days to the first day in the month. For example, DATE(2008,1,35) returns the serial number representing February 4, 2008.