Reading a DOT code: the week, the year and the plant

Every tire built for road use in the United States carries a Tire Identification Number, moulded into the sidewall and preceded by the letters DOT. It is a serial number for a production run, and its last four characters are a date.

The four digits at the end

Two digits for the week of the year, two for the year.

• 5124 — week 51 of 2024.
• 0119 — the first week of 2019.
• 3707 — week 37 of 2007.

Weeks run from 01 to 52 or 53, so the first pair can never exceed 53, which is a quick check that you are reading the right group of digits.

Before 2000 the date was three digits: two for the week, one for the year. 408 means week 40 of a year ending in 8, and which decade it belonged to had to be inferred. Some tires from the 1990s carry a small triangle after the code to mark that decade. Any tire still wearing a three-digit date is, at minimum, from the last century.

The rest of the number

The current standard, in force since a 2015 federal rule, fixes the identification number for new tires at thirteen symbols:

• Three symbols for the plant. The code that identifies the factory, expanded from two symbols because the two-symbol space had run out. Manufacturers were permitted to keep using an existing two-symbol plant code until April 2025, so both lengths remain in circulation on tires already on the road.
• Six symbols chosen by the manufacturer. Internal identification — historically this space held a size code plus an optional descriptive group.
• Four symbols for the date, always last.

Retreaded tires use a shorter seven-symbol number to the same pattern. Fixing the total length was the point of the change: a code of a known length makes a missing or unreadable symbol obvious rather than invisible.

Why one sidewall shows less

Look at both sides of the same tire and you will often find the full number on one and a truncated version — everything except the date group — on the other.

That is a manufacturing artefact. The date portion is formed by a small changeable insert in the mould, swapped as production moves through the weeks, and only one side of the mould carries it. The rule requires the complete number on one sidewall and permits a partial on the other.

The consequence is practical: if the sidewall facing you ends without a four-digit group, the date is on the other side, and on a mounted tire that can mean looking from underneath the vehicle or turning the wheel to full lock.

What the code is used for

• Recalls. Campaigns are issued against identification number ranges, not against model names. The number on the tire is what a recall lookup asks for.
• Registration. Tires bought from a dealer are registered against the buyer, so the manufacturer can make contact if a run is recalled. Independent sellers hand the registration form to the buyer instead.
• Age. The date code is the only source. Tread depth says how much a tire has been used; nothing on the sidewall except those four digits says when it was made.

The three letters in front

DOT is not part of the serial number. It is a certification mark: the manufacturer's statement that this tire complies with the federal motor vehicle safety standards that apply to it. A tire built for another market, or for competition use only, will not carry it — and on those, the identification number is absent or formatted to a different national scheme entirely.

European tires carry an E in a circle followed by a country number and an approval number instead, which encodes the approving authority rather than a production week. Many tires sold internationally carry both marks, in different places on the sidewall.

Age is not mileage

A tire that has sat in a warehouse has aged without wearing. Rubber compounds change with time, temperature and ultraviolet exposure, and several vehicle and tire manufacturers publish their own recommended maximum service age — the published figures differ between them, and each states its own in its owner literature rather than deferring to a single industry number. Where you need one, read the manufacturer's, not a rule of thumb from a forum.

Two situations where this catches people out:

• A new vehicle. Tires are fitted from stock, and a car delivered in 2026 can leave the dealership on tires moulded in 2025. That is ordinary, and the date code is how you know.
• The spare. A full-size or temporary spare that has never touched the road carries the vehicle's original date code for the life of the vehicle, which is frequently the oldest tire anybody owns. Spare tire sizes covers the rest of what is different about it.

Where it sits among the other markings

The identification number is one of four independent things moulded into a sidewall: the size code, the service description, the quality grades and the identification number. None of them is derived from any of the others. The size code page covers the first, UTQG grades the third, and the date code is the only one of the four that changes every week of production.