Short answer

Most watches sold as an "Audemars Piguet perpetual calendar" for a few hundred dollars are not perpetual calendars at all. The dial shows a day, a date, a month, a moonphase and a leap year window, but the mechanism underneath is a basic automatic or quartz base wearing a calendar plate. A genuine perpetual calendar tracks leap years on its own until 2100. If the leap year indicator clicks forward every time you advance the month, the watch is fake.

The reference everyone copies is the Royal Oak Perpetual Calendar 26574, a 41mm steel or gold watch that ran Calibre 5134 until 2024, when AP replaced it with Calibre 7138. Both movements are thin, automatic, and expensive enough that no one is giving them away. That gap is what fakes try to close, and it is where they fall apart.

Why this complication is the hardest one to copy

A perpetual calendar needs a mechanical program that knows 28, 29, 30 and 31 day months plus the four year leap cycle. Building that into a module roughly 4mm thick takes real watchmaking. Copy shops skip it. What they build instead is a single wheel driven off the hour train that carries the day, date and month discs together, with a leap year window painted onto the same disc.

Two quick tests:

• Advance the month by one click. On a genuine piece the leap year hand or aperture stays put for eleven months of the year. On most fakes it moves with every month change.
• Check how you set the calendar. Calibre 5134 has no crown quickset for the date. Every correction runs through recessed pushers set into the case flank. Fakes almost always let the crown do everything.

Dial and subdial tells

• Grande Tapisserie. The raised squares have fine linear striations across the top face. Fakes run shallow, rounded, or the striations go the wrong direction. The pattern should also stop cleanly at the subdial rings instead of printing over them.
• Subdial depth. Genuine subdials sit recessed with a visible step down from the main dial. Fakes are flat and printed.
• Moonphase. The real disc shows a detailed moon against a dark sky. The cheap version is a yellow circle with a face on it.
• Week track. The 26574 carries a week-of-year scale on the outer dial. Many fakes leave it off or make it decorative.
• Logo. Applied white gold on the genuine, sharp edges, mirror polish. Fakes are etched or laser cut with dull edges.

Case, bezel and bracelet

Start with the bezel screws. On steel references they are white gold, and the slot on each one is cut to align with the case. Fakes use steel screws that strip, and the slots land wherever the thread happens to stop. Run a finger along the octagonal bezel edge. Genuine is one crisp chamfer, polished by hand. Fakes are rounded or over-buffed from a polishing wheel.

Thickness is the next check. The 26574 measures about 9.5mm across. A 12mm slab on the wrist is a giveaway, and so is a bracelet that runs straight instead of tapering toward the clasp. Feel the link edges too. Genuine links are beveled, not sharp, and the bracelet flexes without rattling.

Movement and caseback

Calibre 5134 runs at 19,800 vph with roughly 40 hours of reserve and a 22k gold rotor. Through the sapphire back you should see Côtes de Genève on the bridges, perlage on the mainplate and a finished rotor with the AP hallmark. Fakes use a Miyota or a Chinese clone under a printed rotor plate, and the area below the balance is bare.

Serial engraving matters. The number on the caseback rim should match the number on the movement, and the fonts should be consistent. Audemars Piguet keeps an archive and issues digital certificates, so a watch with an activated warranty can be verified. A certificate with a blank or pre-printed date, a box that smells like fresh glue, and papers that look laser printed all point the same direction.

Price math

A steel 26574 asks well north of $60,000 on the secondary market, and gold or ceramic versions run far higher. Nobody sells a working one for $500. If a listing shows a full perpetual dial at a three figure price, the seller is describing a replica, whether they say so or not.

If you are buying a replica on purpose

Judge it on its own terms. Does the calendar actually function, or are the subdial hands frozen? Is the case thin enough to wear under a cuff? Do the subdials sit at the right depth? Does the plating survive daily wear without turning pink at the edges? A decent copy runs a modified automatic with a real day, date and month module, even when the leap year is fake. Anything cheap with a full perpetual dial is a printed dial with hands that never move on their own.