Decode a Seiko serial
Enter the serial engraved on the caseback. Add the movement caliber and we’ll narrow which decade it came from.
Where do I find these numbers?
The serial is engraved on the outside of the caseback (the metal back of the watch). The caliber is the 4-character movement code — it’s the first part of the case reference, e.g. 6309-7040, also stamped on the movement itself.
Type a serial above — the decode appears here instantly, entirely in your browser.
Year
The first character is the last digit of the production year — so it repeats every decade.
Month
The second character is the month: 1–9 for Jan–Sep, then O, N, D for Oct, Nov, Dec.
Sequence
The remaining digits are that month’s production count for the line.
Seiko has never published an official serial-dating standard — this is a community-derived convention. It works for most Seiko (and Seiko 5) watches from 1966 onward, but can mislead on Grand Seiko, some quartz lines, and watches with service-replaced movements. Treat the result as a strong estimate, not a certificate.