Annual Calendar Complication
A calendar tracking month lengths automatically, needing one manual correction per year in February.
The annual calendar is a calendar complication intermediate between the simple date (requiring manual correction at the end of every short month) and the perpetual calendar (which never requires correction except on century non-leap years). An annual calendar automatically adjusts for months of 30 and 31 days but requires the wearer to manually advance the display once per year — at the end of February — because it cannot distinguish between February's 28 or 29 days and the 30-day months. Patek Philippe developed and patented the annual calendar mechanism and introduced it commercially in reference 5035 in 1996. The concept has since been adopted by IWC, Rolex (Sky-Dweller), Chopard, and others under various proprietary mechanisms.
Quick facts
- Type
- Complication
- Complication
- annual-calendar
- Era
- 1996 (Patek Philippe ref. 5035)
- Origin
- Switzerland
Annual Calendar Mechanism Logic
The annual calendar cam encodes 10 months out of 12 correctly: all months except January and February are handled automatically. The cam has steps corresponding to 30-day months (April, June, September, November) that trigger an extra advance from 30 to 1 without pausing at 31. The three 31-day months adjacent to these (March, May, July, August, October, December) advance normally from 31 to 1. February is not encoded in the cam — the mechanism treats February as though it were a 30-day month, so it will stop at 30 rather than jumping to March on the 28th or 29th. Once per year, at midnight of the last day of February, the owner presses the date corrector to advance from the incorrectly displayed 29 (or 30) to March 1.
Patek Philippe Reference 5035
Patek Philippe introduced the first annual calendar wristwatch in 1996 as reference 5035, housing calibre 315/1 AQ. The display showed date, day of week, and month through three apertures in the dial — a design language continued in subsequent references 5036, 5125, 5146, and the current 5205 and 5396. The mechanism uses a jumper and cam system that reads a 10-step profile cam representing the 10 months requiring discrimination (the two non-February months of 30 days and all eight months adjacent to them). Patek Philippe holds the Swiss patent for this specific mechanism; other manufacturers have developed independently different mechanical solutions achieving the same annual correction behavior.
IWC and Rolex Annual Calendar Designs
IWC's Portugieser Annual Calendar uses a different cam architecture than Patek's approach, developed independently and patented separately. The Rolex Sky-Dweller (reference 326935, launched 2012) uses the Saros annual calendar mechanism incorporated in calibre 9001 — Rolex's term for their proprietary annual calendar design. The Sky-Dweller uses an off-centred chapter ring for month display and an annular date ring rather than conventional aperture displays, combined with the Ring Command bezel that allows setting multiple functions via the crown. The Saros mechanism was named after the saros cycle — the 18-year period after which lunar and solar eclipses repeat in near-identical geometry.
Practical Tradeoff vs Perpetual Calendar
An annual calendar movement is mechanically simpler and typically thinner than a perpetual calendar movement — the perpetual calendar's 48-month cam stack and additional lever set for February add height and complexity. For a wearer who is comfortable with one correction per year, an annual calendar provides nearly the same convenience as a perpetual at lower mechanical complexity and often lower cost. For a wearer who wishes never to set the calendar (or who owns a perpetual calendar as a matter of mechanical interest), the perpetual calendar is preferred. Both types require resetting if the watch has been unworn and stopped for several days.
Sources & further reading (3)
- encyclopedia — accessed 2026-05-07
- encyclopedia — accessed 2026-05-07
- watch-reference — accessed 2026-05-07
Frequently asked questions
When exactly does an annual calendar need to be corrected?
At midnight (or early on the morning of) March 1st — after the last day of February. On a standard annual calendar, the date wheel will have advanced to a display of '29' or '30' on the 28th or 29th of February (depending on whether it is a leap year), rather than automatically jumping to March 1. The corrector pusher is pressed to advance from the incorrect February date directly to March 1.
Does the annual calendar handle leap years?
No. The annual calendar treats all Februarys as having 30 days (or sometimes 28 days, depending on the specific mechanism). It does not distinguish between February 28 and February 29 in a leap year. A single manual correction is needed each year — in a leap year, the correction may be a one-step advance from '29' to March 1; in a non-leap year, a two-step advance from '28' or '29' to March 1. The correction method varies by movement design; the owner's manual should be consulted.
How does an annual calendar differ from a simple date?
A simple date display (single date window showing 1–31) does not distinguish between months and requires manual correction at the end of every month with fewer than 31 days — January, March, May, July, August, October, and December have 31 days and require no correction; the other months do. That is seven potential corrections per year for a simple date. An annual calendar requires only one correction per year (at the end of February), reducing the maintenance burden significantly.