Short answer

A fake Patek Philippe perpetual calendar moon phase is a replica of a watch that pairs a perpetual calendar with a moon phase window. The copied references include the 3940, 5140, 5327, 5270, 5320G and 5740/1G. Prices run from about $250 to $1,500. In most replicas the moon disc turns at the right speed. The leap year logic does not.

References that get copied

  • 3940, made 1985 to 2007. 36 mm case. Caliber 240 Q. Day, date, month, 24-hour and moon phase subdials.
  • 5140, made 2006 to 2018. 37.2 mm case. Caliber 240 Q.
  • 5327, introduced 2016. 39 mm case. Caliber 240 Q.
  • 5270, introduced 2011. 41 mm case. Chronograph plus perpetual calendar. Caliber CH 29-535 PS Q.
  • 5740/1G Nautilus, introduced 2018. 40 mm case. Caliber 240 Q.

Moon phase: real numbers

Patek Philippe rates the moon phase on these watches to one day of error in 122 years. That figure comes from the tooth count in the moon wheel and the gearing in the 240 Q.

A standard 59-tooth moon wheel advances at 29.5 days per cycle. The synodic month is 29.53059 days. The gap is 0.03059 days per month, which is about one day of drift every 2.7 years.

Factories that build these replicas do not publish a tooth count. Assume the cheaper wheel. If the replica uses a 59-tooth wheel, expect a correction about every three years. The moon disc on low tier replicas is brass with printed stars. Genuine discs are cut and finished.

Movement

The 240 Q is an automatic with a micro-rotor, 21,600 vph and a 48-hour power reserve. Chronograph perpetual models use the CH 29-535 PS Q.

Replica versions use an Asian automatic with a calendar module stacked on the base movement. Chronograph replicas often use a Seagull ST19, a hand-wound column wheel movement. In many replicas the leap year indicator is decorative. The month changes. The February 29 skip at 2100 does not. That test settles the question in seconds.

Checks on case and dial

  • Thickness. A calendar module adds height, so replica cases run 1 mm to 3 mm thicker than the reference.
  • Case metal. Genuine cases are 18k gold or platinum. Most replicas are steel with plating. Weight differs.
  • Caseback. Look for the reference number, movement number and the Patek Philippe Seal.
  • Subdial print. Month and day fonts sit close to the center on genuine dials. Replica print is wider.
  • Moon aperture. The opening on a 3940 is a shallow arc. Replica openings are deeper and rounder.

Price tiers

Entry replicas with a printed moon disc sell for about $250 to $450. Mid tier runs about $500 to $900 and adds a sapphire caseback. Top tier runs about $1,000 to $1,500 with a cloned 240 Q layout. Genuine 3940 examples trade from about $35,000 to $70,000 at auction. A 5270 runs higher.

US law

18 U.S.C. § 2320 covers trafficking in counterfeit goods. A first offense by an individual carries up to 10 years in prison and a $2 million fine. U.S. Customs and Border Protection can seize and destroy shipments. Patek Philippe holds the trademarks on the name, the Calatrava cross and the reference numbers.

Bottom line

The moon phase is easy to copy. The perpetual calendar mechanics are not. That gap separates a $300 replica from a real 3940.