DoD Shelf-Life Codes (SLC) — Complete Reference

A Shelf-Life Code (SLC) is a one-position code assigned to a National Stock Number that states how long an item keeps and whether that period can be extended. The code answers two linked questions a storekeeper needs before putting materiel on a shelf: does this item deteriorate, and if it does, what happens when it reaches the end of its life — automatic disposal, or inspect-and-extend? The Shelf-Life Code is governed by the DoD Shelf-Life Management Program (DoD Manual 4140.27), administered for the Department of Defense by the Defense Logistics Agency (DLA).

At a glance

• What it is: A one-position code on the NSN identifying the number of months of original shelf life and whether it is non-extendible (Type I) or extendible (Type II).
• Length and format: A single character — 0, an alphabetic letter, or a numeric digit (1–9); the letter X is the special extendible code.
• The three buckets: 0 = not a shelf-life item (non-deteriorative); alphabetic (every letter except X) = Type I, non-extendible; numeric (1–9) and the letter X = Type II, extendible.
• X specifically: The one alphabetic code that is Type II (extendible); in Table 1 its inspect/test interval is 85 percent of the assigned period, and the manual assigns it to extendible/replaceable kits (CASKOs).
• Regulatory source: DoD Shelf-Life Management Program — DoD Manual 4140.27, Volume 1, Section 6, Table 1 (formerly DoD 4140.27-M), administered by DLA; FLIS is the master data record per DoD Manual 4100.39.
• Exact period per code: The full code-to-period mapping is given in the complete code table below, reproduced from DoD Manual 4140.27, Volume 1, Table 1.

What the Shelf-Life Code is

The Shelf-Life Code records the number of months of original shelf life — the period, set when the item is cataloged, after which the materiel must be inspected, tested, restored, or removed from service — and classifies the item as Type I or Type II. That classification is the operational heart of the code:

• Type I — non-extendible. The shelf life is fixed. When it is reached, the item cannot simply be re-certified; it is removed from issue and disposed of (or used) within its period. Type I items carry alphabetic codes — every letter except X.
• Type II — extendible. The shelf life can be extended after a prescribed action — a visual inspection, a certified laboratory test, or a restorative action — confirms the materiel is still serviceable. Type II items carry numeric codes (1–9) and the single alphabetic code X.

Code 0 stands apart: it means the NSN is not a shelf-life item — it is non-deteriorative, has no shelf life, and is not managed under the program at all. Most durable hardware is 0-coded; a non-zero code is the flag that an item is perishable in the supply sense and must be managed on a clock.

Why the Type I / Type II distinction matters

The single most consequential thing the SLC tells a logistician is what happens at expiration:

• For a Type I item, an approaching expiration date means plan to use or dispose of it — the period is fixed and cannot be extended. Letting it expire means losing it.
• For a Type II item, an approaching expiration means schedule the required inspection or test — if the materiel passes, its shelf life is extended and it stays in service. Treating a Type II item like a Type I (disposing of it at first expiration without attempting extension) wastes serviceable materiel; treating a Type I item like a Type II (assuming it can be extended) risks issuing degraded materiel.

This is why the alphabetic-versus-numeric reading is worth internalizing: a letter (except X) means a hard stop; a number or X means inspect-and-extend.

Shelf-Life Code classes

The table below gives the authoritative class structure of the code, confirmed verbatim against the glossary SLC definition in DoD Manual 4140.27, Volume 1. The specific shelf-life period tied to each individual letter and digit follows in the complete code table.

Complete code table

The table below is the complete shelf-life code set, reproduced from DoD Manual 4140.27, Volume 1, Section 6, Table 1 ("Shelf-life Codes"). Each shelf-life period maps to a Type I (non-extendible) code and, where the period is also offered as extendible, a parallel Type II (extendible) code. "N/A" in a Type column means no code of that type is assigned to that period in Table 1.

How shelf-life codes are used

The SLC drives materiel handling from receipt through disposal:

• Receipt and storage. Deteriorative (non-zero) items are stored to support stock rotation — first-in, first-out — so the oldest materiel issues first and nothing quietly expires on the shelf.
• Issue and inventory. The code is checked so that expired or near-expired materiel is caught before issue, and so Type II items due for inspection are routed to the extension process rather than disposed of.
• Extension vs. disposal. The Type I/Type II reading determines the end-of-life action — fixed disposal at the expiration date for Type I, inspect-and-extend at the inspect/test date for Type II. This pairs with the Supply Condition Code (defined in DLM 4000.25-2), which records the materiel's current serviceability and can reflect a shelf-life suspension or expiration.
• Catalog management data. The SLC is carried with the NSN in the federal catalog and is visible through WebFLIS / FLIS alongside the item's other management data, including its unit of issue.

Worked example

A storekeeper receives two line items and checks each item's Shelf-Life Code in the catalog data.

• The first shows 0 — not a shelf-life item. It is shelved as ordinary durable stock with no shelf-life clock.
• The second shows L — an alphabetic code, so Type I, non-extendible. From Table 1, L is a 24-month (2-year) shelf life. The item must be used or disposed of within that fixed period; the storekeeper stores it for first-in-first-out rotation and flags its expiration so it is consumed in time — there will be no extension.

Had the second item instead shown a numeric code or X, it would be Type II, extendible. For example, 5 is a 27-month extendible period: as the inspect/test date approaches, the storekeeper routes the item for the required visual inspection or laboratory test, and if it passes, its shelf life is extended and it stays in service. Same approaching date, completely different action — which is exactly what the code exists to tell you.

Common errors and gotchas

• Treating a Type I item as extendible. Alphabetic codes (every letter except X) are non-extendible; there is no inspect-and-extend path. Assuming one risks issuing degraded materiel.
• Disposing of a Type II item at first inspect/test date. Numeric codes (1–9) and X are extendible — attempt the required inspection or test before disposal, or serviceable materiel is wasted.
• Reading 0 as a short shelf life. 0 means the NSN is not a shelf-life item (non-deteriorative), not "zero months."
• Assuming the alpha codes stop at S. The Type I alphabetic sequence does not end at S — it continues with I (84 months), T, U, W, Y, Z, and V. Letter O is not used, and X is reserved for the Type II (extendible) class. Read the exact period from the complete code table above (DoD Manual 4140.27, Table 1).
• Ignoring storage conditions. Shelf life assumes optimum storage; temperature, humidity, and handling can shorten the usable life regardless of the coded period, which is why shelf-life items are visually inspected before use.

Related codes and cross-references

• Supply Condition Codes (SCC) — the serviceability classification that reflects a shelf-life suspension or expiration on the supply record.
• Unit of Issue (U/I) — how the item is requisitioned and issued; read with the shelf life when planning consumption.
• Navy Cognizance Symbols (COG) — Navy management-data prefix on the NSN that the shelf-life code accompanies.
• WebFLIS / FLIS — the federal catalog data, including shelf-life management data, for an NSN.

Authoritative references

• DoD Manual 4140.27, Volume 1 — DoD Shelf-Life Management Program: Program Administration (July 6, 2016, incorporating Change 2, December 11, 2019). The governing manual; Section 6, Table 1 assigns the shelf-life codes and their periods, and the glossary defines the Type I / Type II / Code 0 structure. Published by the DoD issuances office.
• DoD Manual 4140.27, Volume 2 — DoD Shelf-Life Management Program: Materiel Management. Materiel-management procedures for shelf-life items, via the DoD issuances office.
• DoD Shelf-Life Program. Administered for the Department of Defense by the Defense Logistics Agency.

Last verified

This reference was last reviewed on 2026-06-20 and verified verbatim against DoD Manual 4140.27, Volume 1, Section 6, Table 1 ("Shelf-life Codes") and the manual's glossary (incorporating Change 2, December 11, 2019). Confirmed from the primary source: the code-class structure (0 = not a shelf-life item; every alphabetic code except X = Type I non-extendible; numeric 1–9 and X = Type II extendible) and the complete code-to-period mapping in the table above. Two errors in the prior draft were corrected against Table 1: the Type I alphabetic set does not stop at S (it runs through the alphabet — A–S, then I, T, U, W, Y, Z, V; no O), and the claim that X denotes "military-essential/medical items over 60 months" is not supported by this manual and was removed (X is the single Type II alphabetic code, with an inspect/test interval of 85 percent of the assigned period, assigned to extendible/replaceable CASKO kits per §6.1.c). To suggest a correction, use the site's correction path.