How to date a Seiko from its serial number

Every Seiko carries its birthday on the back. The six-digit serial number on the caseback tells you the year and month the watch was made. Here is how to read it, and a decoder that does it for you.

How the code works

On most Seiko watches from the 1960s onwards, the first two characters of the serial number are the date code:

• First digit = the last digit of the year. A 4 means 1964, 1974, 1984, 1994 and so on.
• Second character = the month. 1 to 9 are January to September. For October, November and December Seiko used O (or 0), N and D.
• The remaining digits are the production number within that month.

Example: serial 455948 → 4 = a year ending in 4, 5 = May. On a Lord Matic 5606, which was made from the late 1960s to the late 1970s, that can only be May 1974.

Which decade? Check the movement

The serial only gives the last digit of the year, so you need the movement to pick the decade. The reference on the caseback, for example 6309-7040, starts with the movement number (6309). Each movement was made for a limited span of years, so usually only one decade fits. The decoder above does this for the most common movements; the years are approximate.

When the serial is worn off

Casebacks get polished and engravings wear away. Shine a torch from the side, almost parallel to the caseback, so the engraving casts shadows. If nothing is left, the dial code and the movement still narrow the date down to a range of years.