Convert Julian Dates (yyddd, yyyyddd, or cyyddd) to Standard Excel Dates

This tool converts Julian-style dates in your selection into standard Excel date values.

Julian dates are often used in data exports from legacy systems and represent dates as a combination of the year and the day of the year:

• yyddd (e.g., 24001 = Jan 1, 2024)
  • Years are interpreted using Excel's 2029 Rule: values below 30 are treated as 2000-2029, values 30 or higher as 1930-1999.
• yyyyddd (e.g., 2024001 = Jan 1, 2024)
• cyyddd (JD Edwards / AS/400 format)
  • The first digit is the century (0 = 1900s, 1 = 2000s)
  • For example: 010015 = Jan 15, 1910; 124015 = Jan 15, 2024

This date format is commonly used in logistics, finance, mainframe systems, and software like JD Edwards and AS/400.

After conversion, the dates become regular Excel date values, which you can use in formulas, formatting, or sorting.

Note:

• This tool follows Excel's default interpretation of two-digit years using the 2029 Rule: https://learn.microsoft.com/en-us/office/troubleshoot/excel/two-digit-year-numbers
• Excel date values are based on the Gregorian calendar, starting from January 1, 1900.
• Although often called "Julian dates" in business and legacy systems, formats like yyddd and yyyyddd are technically known as ordinal dates. This differs from the historical Julian calendar and the astronomical Julian Day Number, which tracks days since 4713 BC and is used by scientists.
• Only values that follow one of the supported formats are converted. Ensure your data is numeric and structured correctly.

Starting this tool

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