A lot number on food packaging is a code that identifies a specific batch of products made at the same time, in the same place, under the same conditions. It’s typically a short string of letters and numbers printed somewhere on the package, and its main purpose is traceability: if something goes wrong with that batch, the lot number lets the manufacturer and regulators track exactly which products are affected and pull them from shelves.
What a Lot Number Actually Tracks
When a food manufacturer produces a product, they don’t make one jar or one bag at a time. They produce in batches, sometimes hundreds or thousands of units in a single run. A “lot” refers to one of these production batches, and the lot number is the unique identifier assigned to it. Every unit in that lot was processed on the same equipment, with the same ingredients, during the same production window.
This matters because if a contamination problem surfaces later, the lot number narrows the issue to a specific group of products rather than forcing a recall of everything the company has ever made. The FDA uses lot codes (formally called “traceability lot codes”) to skip steps in the supply chain and trace a contaminated food back to its source faster. Companies that manufacture, process, pack, or hold certain foods are required to record these codes at every major stage, from harvesting and packing through shipping and receiving at the store.
Where to Find It on the Package
Lot numbers don’t have a single standardized location. You’ll commonly find them printed or stamped on the bottom of cans, on the back or side of boxes, near the seam of bags, or on the neck of bottles. They’re sometimes labeled “LOT,” “LOT #,” or “Batch,” but just as often they appear with no label at all, as a string of characters near the expiration date.
In Europe, lot numbers are sometimes preceded by the letter “L” to distinguish them from other codes on the label. EU law requires the lot indication to be easily visible, clearly legible, and indelible on prepackaged foods. In the U.S., there’s no required “L” prefix, so the lot code can look like just about any combination of letters and numbers.
How Lot Codes Differ From Expiration Dates
This is where most of the confusion comes from. The USDA distinguishes between two types of dating on food labels: “open dating” and “closed dating.” Open dating is the calendar date you’re used to seeing, like “Best By 09/15/2025” or “Use By 03/01/2026.” It’s meant for you as a consumer, giving a readable estimate of when the product is at its best quality.
Closed dating is the lot code. It’s a series of letters and numbers applied by the manufacturer to identify the date and time of production. Unlike a best-by date, it’s not designed to be easily read by shoppers. A lot code like “A2451387” might encode the production plant, the day of the year, the production line, and even the time of day, but you’d need the manufacturer’s key to decode it. Sometimes the two overlap: on egg cartons with a USDA grade shield, for example, the “pack date” is a three-digit number representing the day of the year (001 for January 1, 365 for December 31), which serves both as a date indicator and a lot identifier.
The simplest way to tell them apart: if it’s written as a normal calendar date with words like “best by” or “use by,” it’s for freshness. If it’s an unexplained string of characters, it’s the lot code for traceability.
Common Lot Code Formats
There is no universal format. Each manufacturer creates its own system, which is part of why lot codes look so cryptic. That said, several patterns are common:
- Julian date codes use a three-digit number for the day of the year, sometimes preceded by the last digit of the year. So “5173” could mean the 173rd day of 2025 (June 22).
- YYMMDD or MMDDYY formats embed the production date directly, sometimes followed by a letter or number for the production line or shift.
- Plant and line identifiers are often the first one or two characters, indicating which factory and which production line made the product.
- Time stamps may appear at the end as a two- or four-digit number representing the hour or minute of production.
Can codes, common on canned goods, are a specific type of closed dating that typically combine several of these elements into one short string. The manufacturer knows exactly what each character means, even if you don’t.
Why Lot Numbers Matter During Recalls
Lot numbers become directly useful to you when a food recall is announced. Recall notices include specific identifying details: the product name, packaging size, UPC barcode number, lot codes, sell-by or use-by dates, and sometimes photos of the label. If you hear about a recall, you check the lot number on your product against the numbers listed in the notice. A matching lot number means your specific product is part of the affected batch. A different lot number means your product came from a separate production run and isn’t included.
This precision is the whole point of the system. Without lot codes, regulators would have to recall every unit of a product regardless of when or where it was made. With them, the FDA can pinpoint the contaminated batch, identify every company that handled it, and determine the appropriate scope of the recall. Under current rules, companies must be able to provide this traceability information to the FDA within 24 hours of a request.
How the System Works Behind the Scenes
A lot code is first assigned when a raw ingredient is initially packed or when a food is transformed into something new (think raw tomatoes becoming jarred salsa). From that point forward, every company that ships, receives, or further processes that food is required to record the lot code along with other key details: who they received it from, when, and where. This chain of records follows the food from farm to table.
The FDA’s Food Traceability Rule, part of the broader Food Safety Modernization Act, formalized this system for high-risk foods like leafy greens, fresh-cut fruits, soft cheeses, and certain seafood. The rule applies to domestic and foreign firms producing food for U.S. consumption. At each critical point in the supply chain, from harvesting and cooling to shipping and receiving at retail, the lot code ties the product to a specific time, place, and handler. The goal is straightforward: when an outbreak of foodborne illness occurs, investigators can trace the problem food back to its origin in hours or days instead of weeks.