Seiko serial number lookup

The six characters

A Seiko serial made since the late 1960s has six characters: the first is the last digit of the year, the second the month, the last four a production number[1][2]. The month characters, as the sources give them:

The decade

One digit repeats every ten years, so the serial alone never gives the decade[3][4]. The decoder starts from every year since 1966 that ends in the digit and removes a year only with evidence: outside the calibre’s production years[1], outside the window of its revision letter (7S26A, B, C), outside the model’s years, or before 1976 when the case back has characters in a box[3]. A calibre made for more than ten years leaves two or three candidates; we show them all, with what each one fits.

Where the serial and the calibre leave no year at all, the result says so and stops: one of them, or our production years, is wrong, and we don’t pick which.

Seven characters and the Seiko 5 Sports

Before 1969 Seiko used seven characters, mostly year-month-number but sometimes month-year-number; the decoder shows both readings[1]. The Seiko 5 Sports range of 2019 uses its serial as a plain production number, so it can’t be dated this way[1][2].

What we couldn’t verify

• How the characters after the first two are laid out on a 7-character serial: our sources only give the order of year and month.
• Production end years for most calibres. Without one, every later decade up to the date we checked the rule stays a candidate.
• Production years of case codes (the four digits after the hyphen): not collected yet, so they don’t narrow anything.
• Watchsleuth’s Seiko date finder could not be read (the site refused our requests).