What is a lot number and why does it matter?

A lot number (also called a batch number) is a unique identifier a manufacturer assigns to a specific production run. It matters because it lets you trace every unit back to the exact date, plant, and raw materials it came from — which is the foundation of recalls, warranty claims, expiry management, and regulatory compliance.

How do I read a lot number?

Most lot codes encode the production date first. Common patterns: YYJJJ (year + Julian day, e.g. 25201), YYWW (year + week), or a full date prefix like 20250720. Letters after the date usually identify the plant, line, or shift. Ask your vendor for their key and save it against the vendor profile so anyone on your team can decode it.

Is a lot number the same as a serial number?

No. A lot number identifies a whole production batch (hundreds or thousands of units share it), while a serial number identifies a single unit. Regulated goods often carry both — the lot for the batch, the serial for the individual item.

Which industries are required to track lot numbers?

Food and beverage (FSMA 204), dietary supplements (21 CFR 111), cosmetics (MoCRA), pharmaceuticals (DSCSA), medical devices (UDI), and many industrial goods (RoHS, aerospace) all require lot traceability. Retail marketplaces like Amazon, Walmart, and Target also increasingly require lot data on receiving for FBA and DSD programs.

What is FEFO and how is it different from FIFO?

FIFO (First-In-First-Out) ships the oldest inventory first based on receiving date. FEFO (First-Expiry-First-Out) ships whichever lot expires soonest — which may not be the oldest one received. FEFO is the correct rule for anything with an expiry date. A good WMS supports both and lets you set the rule per SKU or per warehouse.

How does Willowcommerce handle lot tracking?

Willowcommerce tracks lot numbers at receiving, through every bin and warehouse transfer, and onto the outbound shipment. You get FEFO/FIFO pick rules, expiry alerts, one-click recall traces (both directions), and lot-level reporting across all your sales channels — Amazon, Walmart, Shopify, TikTok Shop, and more.

Inventory Guide · 8 min read

How to read and manage lot numbers: a complete guide for inventory managers

Lot numbers are the backbone of recall readiness, expiry management, and regulatory compliance. This guide walks through how to read them, why they matter, and how to track them cleanly through your warehouse — from receiving to the outbound label.

What is a lot number?

A lot number (or batch number) is a unique identifier a manufacturer assigns to a specific production run — every unit produced on the same date, line, and shift shares the same lot. Unlike a serial number, which is per-unit, a lot number groups hundreds or thousands of items that were made together and therefore share the same raw materials and quality history.

If a raw ingredient is later found to be contaminated, a component is recalled, or a batch fails QA in the field, the lot number is what lets you answer: which units are affected, where are they now, and which customers received them?

Why lot number management matters

Recall readiness

Trace every affected unit in seconds instead of days. FSMA 204, DSCSA, and MoCRA all require you to produce this data on request.

Expiry & shelf-life

Sell FEFO (First-Expiry-First-Out) so nothing sits on the shelf past its date — protecting margin and customer trust.

Quality investigations

When a customer complains, the lot number ties the complaint back to a specific run, supplier, and QA record.

Marketplace compliance

Amazon FBA, Walmart WFS, and Target Plus increasingly require lot data on inbound shipments for regulated categories.

Warranty & returns

Confirm whether a returned item is in-warranty and identify systemic defects across a whole production batch.

Audit trail

A clean lot ledger is the single most-asked-for artifact in FDA, USDA, and retail vendor audits.

How to read a lot number

There is no single global standard for lot number formats — each manufacturer chooses their own — but a handful of patterns cover most of what you'll see in the wild.

25201YYJJJ (Julian date)Day 201 of 2025 → July 20, 2025

2529AYYWW + lineWeek 29 of 2025, production line A

20250720-B3YYYYMMDD + line/shiftJuly 20, 2025, line B, shift 3

L25G20-014L + YY + month letter + DD + sequenceJuly (G) 20, 2025, 14th batch of the day

Rule of thumb: always ask each vendor for their lot-numbering key and store it against the vendor record in your system. That way anyone on the receiving team can decode a lot without guessing.

Managing lot numbers end-to-end

1
Locate the lot number on the product or packaging
Lot numbers are typically printed on the outer case, inner carton, or product label — often near the barcode, expiration date, or "LOT" / "L#" / "Batch" prefix. For food, cosmetics, and pharma, it may be laser-etched into the packaging. Always capture the exact string, including leading zeros and letters.
2
Decode the lot number format
Most manufacturers use a structured format that encodes the production date, plant, line, and shift. A common pattern is YYJJJ (year + Julian day), e.g. "25201" = day 201 of 2025 (July 20, 2025). Others use YYWW (year + week) or a full YYYYMMDD prefix. Ask your supplier for their lot-numbering key and store it against the vendor record.
3
Record the lot at receiving
When goods arrive, scan or key the lot number into your WMS on the receiving line — not later at the desk. Attach the lot to the specific quantity received, the PO, the vendor, and the destination bin. If one PO line has multiple lots, split the receipt into one row per lot.
4
Track lots through bins, transfers, and picks
Once a lot is in the system, every movement — bin-to-bin transfer, warehouse-to-warehouse transfer, cycle count, pick — must carry the lot forward. Use FEFO (First-Expiry-First-Out) or FIFO picking rules so the oldest lot ships first and nothing expires on the shelf.
5
Attach the lot to the outbound shipment
When an order ships, write the lot number(s) onto the shipment record and the packing slip. This is the audit trail regulators and retailers ask for during a recall or complaint investigation. If a single order pulls from multiple lots, list all of them.
6
Run a recall or trace in one query
A healthy lot system lets you answer two questions in seconds: "Which orders shipped from lot X?" and "Which lots did customer Y receive?" Run this trace monthly as a fire drill, not for the first time during a real recall.

Best practices for a clean lot ledger

Capture the lot at receiving, on the dock — never "we'll add it later".
Scan, don't type. Manual entry is the single biggest source of bad lot data.
Split receipts by lot: one receiving row per lot, even if it's the same SKU.
Set FEFO as the default pick rule for anything with an expiry date.
Alert on lots within 30 / 60 / 90 days of expiry so you can promote or transfer stock before it ages out.
Run a mock recall every quarter — pick a random lot and trace it in both directions.
Store vendor lot-format keys against the vendor profile.
Print the lot on the packing slip so downstream retailers and end customers can act on it.

Frequently asked questions

Track every lot, every unit, every shipment

Willowcommerce brings lot-level tracking, FEFO picking, expiry alerts, and one-click recall traces into the same platform that runs your multichannel orders and WMS.