A replica Patek Philippe perpetual calendar 3940 is a copy of Patek Philippe's 36mm ultra-thin perpetual calendar, a reference introduced in 1985 and built around the micro-rotor calibre 240 Q. The best replicas reproduce the original's subdial layout: day and 24-hour indication at 9 o'clock, month and leap year at 3 o'clock, and date with moonphase at 6 o'clock. Because the layout is dense and the case is small, the 3940 is one of the harder references to copy well, and the gap between a cheap version and a careful one is easy to see.
Why the 3940 is difficult to replicate
The original is only about 36mm across and roughly 9mm thick, and almost all of that thinness comes from a movement with an off-center micro-rotor sunk into the mainplate. A conventional automatic movement with a full rotor will not fit the same case dimensions, so makers either thicken the case or use a hand-wound or quartz base. That single decision shapes everything else you see on the wrist.
The dial is the second problem. Six functions sit on a small surface, and the subdial rings must be proportioned so the printing stays crisp at arm's length. Moonphase discs are often where budgets show: a flat printed disc with a generic moon reads very differently from a dished disc with a properly shaded moon and stars.
What to check on the case and dial
- Case diameter and thickness: close to 36mm wide and under about 10mm thick. A 40mm version is a different watch, not a 3940.
- Lug shape: slim, gently tapered lugs that curve down toward the strap. Thick or blocky lugs break the profile.
- Subdial positioning: the three counters should sit level with each other and clear of the center hands.
- Moonphase aperture: a clean semicircular cutout with a disc that advances smoothly.
- Hands and markers: applied baton markers, faceted dauphine hands, and printing that stays sharp under magnification.
- Caseback: the 3940 is a solid-back watch, so a display back is a departure from the original design.
- Strap and buckle: alligator-grain leather and a pin buckle that matches the case finish.
Movements used in replica 3940s
Three broad approaches show up in the market. Quartz versions keep the case thin and the price low, but the seconds hand, if present, ticks and the calendar will not behave like a mechanical perpetual. Hand-wound mechanical versions offer a smooth sweep and a thin profile, and some include a functioning moonphase driven off the hour wheel. Automatic versions with a modified calendar module can look convincing from the front but usually add thickness.
Ask what the movement is before you buy, and ask how the calendar is set. A true perpetual calendar mechanism accounts for leap years on its own. Many replicas use an annual or simple calendar module dressed to look perpetual, which means you correct the date at the end of shorter months.
Price tiers and what they buy
Entry-level replica Patek Philippe perpetual calendar 3940 models tend to use quartz movements and printed dials, and they are best treated as costume pieces. Mid-tier versions move to mechanical movements and better dial printing, and this is where most buyers land. The top tier focuses on case finishing, correct subdial proportions, a dished moonphase disc, and hand-finished bridges visible through an opened back. Pay for the details you can actually see and feel, not for a label on a listing.
Legal and resale considerations
In the United States, selling a counterfeit watch as genuine is illegal, and importing or trafficking in counterfeit goods carries legal exposure. A replica is not a Patek Philippe, cannot be serviced by the brand, and has no collector resale value. Buy only from sellers who describe the item as a replica, keep the description on record, and never pass the watch on as an original. If owning a genuine perpetual calendar matters to you, the secondary market is the honest route, and auction records for the reference are publicly available.
Quick checklist before ordering
- Confirm case size and thickness in millimeters, not in photos.
- Ask for a close-up of each subdial and the moonphase disc.
- Ask for the movement type and how the calendar is adjusted.
- Check the return policy and whether the watch ships with the strap shown.
- Confirm the seller labels the item as a replica in writing.
The 3940 rewards patience. A well-proportioned replica with a thin case, balanced subdials, and a believable moonphase looks far closer to the original than a larger, thicker watch with a busier dial.