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The Complete Guide to Calendar Watches

Piaget Polo Perpetual Calendar Ultra-Thin

Knowing the time is only one thing a watch can do. Sure, it’s the one we use more than any other, but more complicated calendar watches can tell us the date, too. Some can even factor in the day of the week. There are some however that go even further, loading the dial with the information you’d normally only find on your calendar – not only the day and date, but month and in some cases, years.

These calendar watches are among the most impressive complications in the watch world. However, not all are built the same, with varying layers of complexity, usefulness and, of course, price. So, read on if you want a guide to knowing the differences between the various types of calendar watches, the levels of complexity that makes them so extraordinary and why perpetual doesn’t always mean perpetual. Don’t forget to check out our favourite calendar watches from last year while you’re at it.

Complete Calendar

IWC Portofino Complete Calendar

IWC Portofino Complete Calendar

The simplest of the calendar complications – if anything showing this much information could be described as ‘simple’ – the complete calendar (sometimes called the triple calendar) is the first offering the almost full suite of day, date and month. They’re considered the entry level in that it’s relatively straightforward in conception: it marks off 31 24-hour periods, before restarting for the next month.

Unfortunately, our calendar is weird and not every month has 31 days. In fact, if you learned your rhymes at school, you’ll know that five of them don’t: February, April, June, September and November. This means that your complete calendar watch needs to be adjusted five times a year. Oh the inconvenience.

Vacheron Constantin Complete Calendar

Vacheron Constantin Complete Calendar

This fact is actually what really separates all three of the main calendar complications. It’s relatively straightforward to add more wheels onto the date; it’s a whole other matter to take into account shorter months and the absolute weirdo that is a leap year. For those of us less concerned with that level of accuracy however, or obsessively keeping the watch wound, the complete calendar offers plenty of useful information – sometimes also including a moon phase – at a far more accessible price point.

Annual Calendar

A. Lange & Sohne 1815 Annual Calendar

A. Lange & Sohne 1815 Annual Calendar

While it’s easy for us to remember which months have 31 days and which oddities have 30, it’s a lot more difficult for a mechanical watch that really, really wants to keep things nice and regular. So, in order to account for the variation, the movement has to be ‘programmed’. Obviously, that doesn’t involve linking a Lange to an app on your phone; instead, it’s done with a weirdly shaped month wheel.

This wheel has specific notches denoting the shorter months so that, when one of those months appears, the movement understands to skip day 31 and move straight onto the next month.

Patek Philippe 5035

Patek Philippe 5035

Surprisingly, this is actually more recent a complication than its bigger brother, invented as it was in 1996 by Patek Philippe in the Ref. 5035, and only needs to be adjusted for February. That particular version’s not the be-all and end-all however, as there is a version of the annual calendar that also takes a 28-day February into account (Audemars Piguet calls it the Quadriennium) but the concept’s the same. Neither factors in the four-year leap year cycle.

The end result is that most annual calendars need to be adjusted once a year and the February-programmed version once every four years. Those four years however are the difference between the annual calendar and true high complication status.

Perpetual Calendar

Thomas Mudge
Thomas Mudge Perpetual Calendar

Thomas Mudge invented the perpetual calendar pocket watch in 1764

It’s a point of pride that no matter what anyone tells you, the perpetual calendar mechanism was developed by British watchmaker Thomas Mudge. Others might say Abraham Louis Breguet (if you ever get asked who invented a complication, he should be the default answer) and he definitely popularised it in the courts of France, but it’s Mudge that got there back in 1762 and it was put in a wristwatch in 1925 by, of course, Patek Philippe in the 97975.

Patek Philippe First Perpetual Calendar 1898

Patek Philippe 97975 (the first perpetual calendar wristwatch) introduced in 1925

So, as you’ve already surmised, the difference between a perpetual calendar and the rest of its less sophisticated ilk is the fact that it takes into account a leap year. So, it’s worth briefly going over what a leap year actually is.

Basically, it comes from forcing our calendar to fit nature. A year might seem 365 days long, but the Earth actually takes 365.25 (ish) days to orbit the sun. This means that if left to its own devices, the Gregorian calendar would gradually shift out of sync with the seasons as our place in the solar system makes a nuisance of itself. So, we came up with the little cheat of adding an extra day to February every four years. It’s a simple trick for most of us to grasp; a watch, less so.

Audemars Piguet Royal Oak Perpetual Calendar 41mm Blue Ceramic

Audemars Piguet Royal Oak Perpetual Calendar

There are actually a number of ways to make the concept work. They can have a 48-month cam instead of the usual 12-month, with an extra level of notch for the anomalous 29-day February. You can have a 12-month wheel a la the annual calendar, but with a separate cam for the leap year that makes one revolution every four years. Or you can integrate a Maltese Cross satellite to manage February. This last option is particularly cool. It’s basically a square integrated into the 12-month wheel with a protrusion on one side. Every year, it’s forced to make a 90 degree turn so that, on a leap year, the protrusion makes the movement count 29 instead of 28.

No matter how they’re done, perpetual calendars are a work of sheer mechanical ingenuity – with a price tag to match. They’re the pinnacle of what most brands offer, with grand maisons like Patek Philippe, Vacheron Constantin and Audemars Piguet offering gorgeous versions, while independent watchmakers get ever more outlandish with the concept.

Secular Perpetual Calendar

Andersen Geneve Secular Perpetual Calendar
Andersen Geneve Secular Perpetual Calendar Back

Andersen Geneve Secular Perpetual

The problem with most perpetual calendars is that they’re not actually perpetual. You see, another quirk with our not-at-all-confusing calendar is that centurial years – years ending in 00 – are only leap years if they themselves are divisible by 400.

In the obsolete Julian calendar, this wasn’t the case, and every four years was a leap year, regardless. This however gave us too many leap years, shifting us forwards in seasons rather than compensating. This is why we now use the Gregorian calendar (introduced in 1582 by Pope Gregory XIII), which adds the ‘divisible by 400’ rule. So this means that the year 2000, 2400 and 2800 are leap years; the centurial years between are not. perpetual calendars therefore need to be adjusted to compensate. A secular perpetual calendar however, does not.

Furlan Marri Secular perpetual calendar Only Watch 2023

Furlan Marri Secular Perpetual Calendar, Only Watch 2023

The most recent example of a Secular perpetual calendar is the Furlan Marri Piece Unique, created for Only Watch 2023 (soon to be Only Watch 2024, pending their finances). They achieved the concept using the integrated Maltese Cross method on a wheel that counts 100 years. It’s an inspired take, and one that only needed five new parts added onto the ‘base’ perpetual calendar.

Given Furlan Marri’s usual place as an uber- accessible watch brand and the resurgence of calendar watches in general, this likely won’t be the last time we see Secular perpetual calendars in the near future.

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About the author

Sam Kessler

Legend has it that Sam’s first word was ‘escapement’ and, while he might have started that legend himself, he’s been in the watch world long enough that it makes little difference. As the editor of Oracle Time, he’s our leading man for all things horological – even if he does love yellow dials to a worrying degree. Owns a Pogue; doesn’t own an Oyster Perpetual. Yet.