The New IWC ‘Proset’ Perpetual Calendar: Pros, Cons, And How It Works

Years ago, when the mechanical watch renaissance was really gathering steam, IWC’s Kurt Klaus, the legendary engineer who oversaw IWC’s rise to fame as a maker of complications, developed a perpetual calendar unlike anything seen before.

Kurt Klaus, on his 90th birthday

Prior to 1985, perpetual calendars had been delicate complications requiring care in setting, and each indication had to be set individually, using a small tool to press on recessed pushers set into the case.

In that year, however, IWC debuted a new Kurt-Klaus designed perpetual calendar, in which all of the indications could be set just by using the crown. Turning the crown would simultaneously advance all of the calendar indications, so that the:

• Month
• Date
• Day of the week
• Moonphase
• And four digit year display 

… would all advance at the same time, one day at a time.

This was a completely new development in perpetual calendars. Since then, other systems have been developed for so called synchronized perpetual calendars, but the very first was from IWC, in the Da Vinci Perpetual Calendar.

The advantages are obvious: no pushers, no need to use a tool, fewer parts, better reliability, and very easy to set:

Downsides? Only one. The calendar can only be set forwards, not backwards. This means that if you accidentally set the calendar too far ahead, you have to wait until the actual date catches up. However, IWC clearly felt that it was time to update the design, and this year, the “Proset” perpetual calendar movement, caliber 86225, was launched, in three new watches:

• Big Pilot’s Watch Perpetual Calendar Proset “Le Petit Prince” Ceramic
• Big Pilot’s Watch Perpetual Calendar Proset “Le Petit Prince” Stainless Steel
• … and the Big Pilot’s Watch Perpetual Calendar Proset, Stainless Steel

The Proset perpetual calendar movement has all the classic layout and features of the preceding IWC perpetuals, but with one major difference: The calendar indications can now be set both forwards and backwards.

This might seem like a relatively minor update, but it required an almost total redesign of the perpetual calendar mechanism. A classic perpetual calendar knows when to switch the date, thanks to a circular gear with irregular steps on its edge – one step for each month of the year. The depth of the steps determines when the date will switch – on the 31st, seven times per year, the 30th, four times per year, and in February, once per year. Each step switches the date and month indications via a complicated system of spring loaded levers, and both the springs and levers are complicated to make and require much skill to adjust.

Normally February has 28 days, but once every four years, an extra day is added. This is because the calendar gradually falls behind the actual position of the Sun every year, and after four years, the calendar is a full day behind. The 29th of February adds this missing day back in – otherwise we would eventually end up celebrating the Fourth of July in the winter.

The gear with steps for each month is called a program wheel. Although the original IWC perpetual calendar from 1985 was revolutionary in automatically synchronizing all indications, it still used a traditional program wheel and so could not be set backwards.

The IWC Proset perpetual calendar mechanism. The 31 tooth program wheel is held in tweezers, at 3:00. Gears for the perpetual calendar are made using LIGA, a lithography and electroplating technique.

For 2026, the new Proset Perpetual calendar uses a completely different system. The Proset perpetual calendar has a program gear, which makes one rotation per month. The 31 teeth of the gear switch the date daily, but there is a set of three extra teeth, mounted on flexible metal blades. How many of these teeth stick out, controls how many days are skipped over at the end of the month:

• No teeth: no days skipped (full 31 day months)
• One tooth: one day skipped (30 day months)
• Two teeth: two days skipped (29 day month of February in a Leap Year)
• Three teeth: three days skipped (28 day month of February in a non-leap year)

The position of the teeth is controlled by a cam with smooth bumps, or lobes, extending from it. This means that it can be rotated forwards or backwards easily, and since switching the indications is done with only gears, not the complicated lever and spring system of traditional perpetuals, setting the indications forwards or backwards isn’t a problem.

Clockwise from lower left, the thousand year, century, decade, and year disks for the four digit year display

There are a total of five patents connected to the new perpetual calendar – three are for the switching and correcting mechanism itself; one is for the way in which the four digit year display is switched; and one is for the moonphase, which has been modified to work with the new system, and which has a precision of only one day’s error in 1,040 years.

Is this the only perpetual calendar that can be set from the crown both ways? No. IWC was the first, but since 1985, companies like Audemars Piguet, Ulysse Nardin, Moser, and Ochs und Junior have also developed such calendars. Cartier’s discontinued 2014 Rotonde de Cartier Astrocalendrier used a similar system of flexible teeth as well.

Are there any disadvantages to the system? Just one. If the watch is significantly behind the actual calendar date, it might be necessary to turn the crown many times in order to get the date set correctly. However, the design ensures that since switching is smooth, there will be very little actual friction in the watch.

Will the watch always show the right calendar date, without needing correction? Yes. The only exception will be in the year 2100, when the calendar skips the 29th of February even though by the calendar’s rules, it should be a Leap Year.

The 1916 Company is proud to be an authorized retailer for IWC Schaffhausen watches. See the new Proset perpetual calendars here; and contact us for pricing and availability.