Converting Dates to Julian Date Formats in Excel Formula

Julian date format is a way of representing a date by combining the year and the ordinal day of the year. For example, the date January 1, 2021 can be written as 2021001 in Julian date format, where 2021 is the year and 001 is the first day of the year. Similarly, the date December 31, 2021 can be written as 2021365, where 365 is the last day of the year.

There are different variations of Julian date format, such as using two-digit or four-digit year, and padding the day number with zeros or not. For instance, the date January 1, 2021 can also be written as 21001, 21-001, 2021-001, or 2021-1, depending on the preference.

Julian date format is useful for sorting and comparing dates, as well as performing calculations with dates, such as finding the difference between two dates or adding a number of days to a date.

Procedures

In Excel, there is no built-in function or format to convert a date to a Julian date format. However, we can use a combination of other functions and formulas to achieve this task. Here are some examples of how to convert a date to a Julian date format in Excel:

• To convert a date to a Julian date format with two-digit year and three-digit day, padded with zeros, use this formula:

=TEXT(B5,"yy")&TEXT(B5-DATE(YEAR(B5),1,0),"000")

where B5 is the cell that contains the date. This formula works by extracting the two-digit year from the date using the TEXT function, and subtracting the last day of the previous year from the date using the DATE and YEAR functions. Then, it pads the day number with zeros using another TEXT function, and concatenates the year and the day using the ampersand (&) operator.

• To convert a date to a Julian date format with four-digit year and three-digit day, padded with zeros, use this formula:

=YEAR(B5)&TEXT(B5-DATE(YEAR(B5),1,0),"000")

where B5 is the cell that contains the date. This formula is similar to the previous one, except that it uses the YEAR function to get the four-digit year from the date.

• To convert a date to a Julian date format with two-digit year and three-digit day, without padding, use this formula:

=TEXT(B5,"yy")&B5-DATE(YEAR(B5),1,0)

where B5 is the cell that contains the date. This formula is similar to the first one, except that it does not use the TEXT function to pad the day number with zeros.

• To convert a date to a Julian date format with four-digit year and three-digit day, without padding, use this formula:

=YEAR(B5)&B5-DATE(YEAR(B5),1,0)

where B5 is the cell that contains the date. This formula is similar to the second one, except that it does not use the TEXT function to pad the day number with zeros.

Explanation

To understand how these formulas work, let’s take a closer look at each component and see how they operate on an example date, such as January 15, 2021.

• The TEXT function takes a value and a format code, and returns the value as text in the specified format. For example, TEXT(B5,"yy") returns the two-digit year of the date in B5 as text, such as “21”. Similarly, TEXT(B5-DATE(YEAR(B5),1,0),"000") returns the three-digit day of the year of the date in B5 as text, padded with zeros, such as “015”.
• The YEAR function takes a date and returns the year as a four-digit number. For example, YEAR(B5) returns the year of the date in B5 as a number, such as 2021.
• The DATE function takes a year, a month, and a day, and returns a date. For example, DATE(2021,1,1) returns the date January 1, 2021. If the day argument is zero, the DATE function returns the last day of the previous month. For example, DATE(2021,1,0) returns the date December 31, 2020.
• The ampersand (&) operator joins two values together as text. For example, "21"&"015" returns the text “21015”.
• To get the day of the year of a date, we need to subtract the last day of the previous year from the date. For example, to get the day of the year of January 15, 2021, we need to subtract December 31, 2020 from January 15, 2021. This can be done by using the DATE and YEAR functions, as follows:

B5-DATE(YEAR(B5),1,0)

where B5 is the cell that contains the date January 15, 2021. This formula returns the number 15, which is the day of the year of January 15, 2021.

• To convert a date to a Julian date format, we need to combine the year and the day of the year as text, using the TEXT and ampersand (&) functions. For example, to convert January 15, 2021 to a Julian date format with two-digit year and three-digit day, padded with zeros, we need to use this formula:

=TEXT(B5,"yy")&TEXT(B5-DATE(YEAR(B5),1,0),"000")

where B5 is the cell that contains the date January 15, 2021. This formula returns the text “21015”, which is the Julian date format of January 15, 2021.

Example

Suppose we have a list of dates in column A, and we want to convert them to Julian date formats in column B. We can use any of the formulas discussed above, depending on the desired format. For example, if we want to use the format with two-digit year and three-digit day, padded with zeros, we can use this formula in cell B2:

=TEXT(A2,"yy")&TEXT(A2-DATE(YEAR(A2),1,0),"000")

where A2 is the cell that contains the date January 1, 2021. This formula returns the text “21001”, which is the Julian date format of January 1, 2021. Then, we can copy the formula down to the other cells in column B, and we will get the following result: