Julian Date Calendar (Ordinal Date) — Complete Reference

In military logistics, the "Julian date" is the ordinal date — the day of the year, numbered 001 (January 1) through 365 (December 31), or 366 in a leap year. Its most common appearance is inside a MILSTRIP document number, where the date is written in a four-digit YDDD form: one digit for the year and three for the day of the year. This page gives the perpetual ordinal-date calendar — the day number that begins each month, for both common and leap years — and the simple arithmetic to convert any calendar date to or from its ordinal day. Note up front: this is not the astronomical Julian Day Number; in supply, "Julian date" means the day-of-year.

At a glance

• What it is: The ordinal date — the day of the year (001–365, or 366 in a leap year).
• Format in supply: Four digits, YDDD — one year digit followed by the three-digit day of the year (for example, 3175).
• Where it is used: The date field of the MILSTRIP document number; throughout DoD requisitioning and transaction records.
• Regulatory source: The document-number format is defined in MILSTRIP (DLM 4000.25-1); the ordinal numbering itself is the standard day-of-year calendar.
• Leap-year rule: February 29 is day 060; every day from March 1 onward is one higher than in a common year.
• Not to be confused with: The astronomical Julian Day Number (a continuous count since 4713 BC), which is unrelated.

What the Julian (ordinal) date is

The ordinal date answers a single question — "which day of the year is it?" — with a number from 001 to 365 (or 366). January 1 is 001, February 1 is 032, July 4 is 185 (common year), and December 31 is 365 (or 366). Because it is a single number that increases through the year and resets each January 1, it is compact to store and trivial to sort, which is exactly why DoD supply adopted it for transaction dating decades ago.

The name is a historical quirk. The astronomical Julian Day Number is a continuous day count astronomers use, running to seven digits and never resetting. The logistics "Julian date" borrowed the name but is a different thing entirely: it is just the day-of-year ordinal date, and it resets annually. In any DoD supply context, "Julian date" means the ordinal date — never the astronomical count.

The Julian date in the MILSTRIP document number

The Julian date's workhorse role is as the date field of the MILSTRIP document number — the fourteen-character identifier that tags a requisition and travels with it through the supply system. The document number is built from three parts:

1. Positions 1–6 — the DoDAAC. The originating (or owning/screening) activity's DoD Activity Address Code, identifying who created the document.
2. Positions 7–10 — the Julian date (YDDD). The date the document was created: one digit for the year, three for the day of the year.
3. Positions 11–14 — the serial number. A four-character serial that makes the document number unique for that activity on that day.

So a document number such as F123453175U001 parses as DoDAAC F12345, Julian date 3175 (a year ending in 3, day 175), and serial U001.

The single year digit keeps the field compact but makes the year ambiguous across decades — 3175 could be 2023, 2013, 2003, and so on — resolved only from the transaction's real processing window. Some DLMS contexts therefore use an expanded seven-digit ordinal date (YYYYDDD) with the full four-digit year, removing the ambiguity where the extra width is available.

Leap years

A leap year has 366 days because February has 29. The consequences for the ordinal date:

• January 1 – February 28 (days 001–059) are identical in common and leap years.
• February 29 exists only in a leap year and is day 060.
• March 1 through December 31 are each one higher in a leap year than in a common year — March 1 is 061 (not 060), and December 31 is 366 (not 365).

When you read or compute a Julian date for any date from March 1 onward, you must know whether the year is a leap year and use the correct column below. Leap years are those divisible by 4, except century years not divisible by 400 (2000 was a leap year; 1900 and 2100 are not).

Perpetual ordinal-date calendar

To convert any date, take the ordinal day on which its month begins from the table below, then add the day of the month minus one. The table is exact for every year — only the March-onward values differ between common and leap years.

The last day of the year is 365 (common) or 366 (leap). These month-start values are fixed arithmetic — the cumulative day counts of the calendar — and are exact for any year once you know whether it is a leap year.

How to convert a date

Calendar date → ordinal day: start with the month's beginning day (from the table), add the day of the month, subtract one.

• July 4, common year: July begins at 182; 182 + 4 − 1 = 185.
• March 1, leap year: March begins at 061; 061 + 1 − 1 = 061.
• December 25, common year: December begins at 335; 335 + 25 − 1 = 359.

Ordinal day → calendar date: find the largest month-start value that is not greater than your ordinal day; the date is in that month, on day (ordinal − month-start + 1).

• Day 200, common year: the largest start not over 200 is July (182); 200 − 182 + 1 = 19 → July 19.
• Day 061, leap year: the largest start not over 061 is March (061) → March 1. (In a common year, day 061 falls in March as well: 061 − 060 + 1 = 2 → March 2 — the one-day shift in action.)

Worked example — dating and reading a requisition

A supply clerk builds a requisition on June 24 of a year ending in 3 (a common year). To construct the document number:

1. The unit's DoDAAC is F12345 (positions 1–6).
2. The Julian date is 3175 — year digit 3, and June 24 = June's start 152 + (24 − 1) = 175 (positions 7–10).
3. The system assigns serial U001 (positions 11–14).

The resulting document number is F123453175U001. Weeks later, anyone reading that document number can recover the creation date: strip the DoDAAC and serial, read 3175 as "day 175 of a year ending in 3," and — knowing the requisition is recent — resolve the decade to read June 24, 2023. Had the year instead been a leap year ending in 4, the same June 24 would be Julian 4176, because June begins at 153 in a leap year (152 + 1 for the extra February day).

Common errors and gotchas

• Forgetting the leap-year shift. From March 1 on, a leap year's ordinal days are one higher. Using the common-year value for a leap-year date (or vice versa) puts every date off by one.
• Reading the single year digit as unambiguous. YDDD carries only the last digit of the year, so the decade must come from context. Do not assume the current decade when reconciling old documents.
• Confusing it with the astronomical Julian Day. The seven-digit astronomical count is unrelated; in supply, "Julian date" is always the day-of-year.
• Mixing YDDD and YYYYDDD. The compact MILSTRIP document-number date is four digits (YDDD); some DLMS data carries a seven-digit ordinal date (YYYYDDD). Confirm which width a field uses before parsing.
• Day-of-month off-by-one. The conversion adds the day of the month minus one to the month-start value (because the first of the month is the start day itself). January 1 is 001, not 002.

Related codes and cross-references

• Document Identifier Codes (DIC) — the MILSTRIP transaction-type codes carried on the same document the Julian date dates.
• Routing Identifier Codes (RIC) and the DoDAAC — the addressing and routing identifiers that make up the rest of the document number.
• DAASINQ & eDAASINQ — the DLA Transaction Services inquiry tools used to look up the document numbers (and their Julian dates) that DAAS routes.

Authoritative references

• MILSTRIP — Military Standard Requisitioning and Issue Procedures (DLM 4000.25-1). Defines the document-number format, including the four-digit Julian date field, published through the Defense Logistics Agency, Defense Data Standards.
• Defense Logistics Management Standards (DLM 4000.25). The governing data-standards framework under which MILSTRIP document numbering is administered.
• DLA Transaction Services — Defense Automatic Addressing System (DAAS). Routes the MILSTRIP transactions the Julian date is carried in; see DLA Transaction Services.

Last verified

This reference was last reviewed on 2026-06-21. The perpetual ordinal-date calendar and the date-conversion arithmetic are deterministic and exact (verified by computation); the MILSTRIP document-number composition (DoDAAC + YDDD + serial) is confirmed against DLA's published MILSTRIP manual (DLM 4000.25-1) and corroborated by GSA's MILSTRIP Instructions and NAVSUP P-409. To suggest a correction, use the site's correction path.