Julian Date Converter for Lot Codes and Best-By Dates

How to Read a Julian Date Code

A Julian date code is the day of the year, 001 to 365 (366 in a leap year), printed with some or all of the year. Manufacturers use it as the production or pack date in lot codes because it is short and sorts in date order. 24297 is the 297th day of 2024: October 23, 2024.

Letters and extra digits around the date usually name the plant, line or shift. In L24297 B2, the date is 24297 and L and B2 identify the line and batch. The converter reads the digits and shows the rest separately.

Which Year Is a 4-Digit Code?

A YDDD code such as 4297 carries only the last digit of the year, so it fits 2014, 2024 and 2034 equally. For a production date the converter takes the most recent year ending in that digit, since nothing is made in the future. For a best-by date it takes the year within five years of today. When the result is still in doubt, it says so and lists the other decade, so a receiving clerk can check it against the case.

Leap Years Move Every Date After February

Day 60 is March 1 in 2026 but February 29 in 2024. Printed Julian calendars come in two versions for this reason, and using the wrong one puts every spring and summer code a day out. The calendar on this page switches with the year you pick, and day 366 is rejected in any year that does not have one.

Lot Codes, Best-By Dates and Barcodes

The USDA calls Julian codes closed or coded dates: packing numbers for tracking and recalls, not a safety date for the shopper. On a GS1-128 case label the same information is in plain YYMMDD form under application identifiers (10) batch or lot, (11) production date, (15) best before and (17) expiry, listed in the GS1 application identifier reference. Foods on the FDA Food Traceability List also need a traceability lot code under the FSMA 204 traceability rule.

On an 856 ship notice the lot travels in the LIN segment with qualifier LT and the expiration date in DTM*036; check one with the EDI Inspector. Build the case label itself with the SSCC label generator, check the GTIN on it with the check digit calculator, and convert cases to eaches with the unit of measure converter.

The Astronomical Julian Day

Astronomers count days continuously from noon UTC on January 1, 4713 BC, so January 1, 2000 at noon is Julian Day 2451545. It has nothing to do with lot codes, but it shares the name. The Julian Day tab converts it both ways, and the US Naval Observatory converter covers dates before 1900.