A Julian date is sometimes used to refer to a date format that is a combination of the current year and the number of days since the beginning of the year. For example, January 1, 2007 is represented as 2007001 and December 31, 2007 is represented as 2007365. Note that this format is not based on the Julian calendar.
There is also a Julian date commonly used in astronomy, which is a serial date system starting on January 1, 4713 B.C.E.
There are several ways to insert Julian dates.
What do you want to do?
Enter today as a Julian date
To do this task, use the TEXT, TODAY, and DATEVALUE functions.
Example
The example may be easier to understand if you copy it to a blank worksheet.
How to copy an example

Create a blank workbook or worksheet.

Select the example in the Help topic.
Note: Do not select the row or column headers.
Selecting an example from Help

Press CTRL+C.

In the worksheet, select cell A1, and press CTRL+V.

To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.


Notes:

The current date used is taken from the computer's system clock.

In the formulas above, the year begins on January 1 (1/1). To convert the formulas to use a different starting date, edit the portion "1/1/" to the date that you want.
Function details
Convert a date to a Julian date
To do this task, use the TEXT and DATEVALUE functions.
Example
The example may be easier to understand if you copy it to a blank worksheet.
How to copy an example

Create a blank workbook or worksheet.

Select the example in the Help topic.
Note: Do not select the row or column headers.
Selecting an example from Help

Press CTRL+C.

In the worksheet, select cell A1, and press CTRL+V.

To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.


Note: In the formula above, the year begins on January 1 (1/1). To convert the formulas to use a different starting date, edit the portion "1/1/" to the date that you want.
Function details
Convert a date to a Julian date used in astronomy
This formula only works for dates after 3/1/1901 and in workbooks that use the 1900 date system.
Example
The example may be easier to understand if you copy it to a blank worksheet.
How to copy an example

Create a blank workbook or worksheet.

Select the example in the Help topic.
Note: Do not select the row or column headers.
Selecting an example from Help

Press CTRL+C.

In the worksheet, select cell A1, and press CTRL+V.

To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.


Note: You can format the dates as numbers. Select the cell, and on the Home tab, in the Number group, click the arrow, and then click Number.