How Seiko dates its watches
For most Seiko watches made since the 1960s, the serial number on the caseback encodes the production date:
1st character = last digit of the year (e.g. 4 → 1974, 1984, 1994, 2004, 2014, 2024)
2nd character = month: 1–9 for January–September, O (or 0) for October, N for November, D for December
The rest = production number
So 4N1234 was made in November of a year ending in 4. Because the year digit repeats every ten years, you need one more clue to pick the decade.
Narrowing the decade
- Movement calibre. The first part of the model number (e.g. 6309, 7S26, 4R36) is the movement. Each calibre was made only in certain years — enter it above for known ones.
- Dial and case style, such as “Made in Japan” vs “Made in Malaysia”, and the Seiko logo style, also date a watch.
- The production date stamped inside on the movement of some vintage models — a watchmaker can check this when servicing.
Spotting a “frankenwatch”
Vintage Seikos are often rebuilt from parts. If the caseback date, calibre and dial style point to very different years, parts may have been swapped. That doesn’t make a watch bad, but it affects collector value.
Questions people ask
Does this work for Grand Seiko?
Grand Seiko uses a different serial system on many models; this decoder is for regular Seiko, Seiko 5, Presage, Prospex and vintage Seiko.
My serial has letters in both places. What now?
Some modern Seiko serials use a different pattern. If the second character is not 1–9, O, N or D, the date cannot be read this way.
Is the caseback date always correct?
It is the date the case was stamped. If a caseback was replaced, it may not match the movement.
Sources
Results are estimates to help you plan. Always confirm important numbers with the seller, carrier or authority concerned. Last reviewed: November 2026.