A replica Patek Philippe perpetual calendar moon phase costs $300 to $1,200. Most do not track leap years. Three checks decide value: a working leap year indicator, moon phase gear count, and case thickness.

What a Perpetual Calendar Does

A real Patek Philippe perpetual calendar has 275 to 330 parts. Its gear train knows 28, 29, 30, and 31 day months. It adds a leap day each four years. It needs one manual correction in 2100. Patek ref. 3940 (1985 to 2007) set the layout copied by most replicas: date at 3, month and leap year at 12, moon phase at 6, day and night at 9.

Most replicas use a base movement plus a module. Common bases: Miyota 9015, Seagull ST19, ETA 2892, and Hangzhou 6300. The module adds subdials. Many modules lack a leap year cam. The leap year hand stays fixed. The month wheel jumps two positions at once on some units.

Moon Phase Accuracy

Patek moon phase discs use 135 teeth. That ratio loses one day in 122 years and 48 days. Most replica moon phase discs use 59 teeth. A 59-tooth disc loses one day in 2.7 years. Some cheap replicas use a printed disc that never moves. Check the aperture shape: the genuine part forms a lens with two overlapping circles. Many replicas cut a single circle. Test the moon phase: forward the hands 30 days and count the moon moves. A 29.5 day cycle is wrong. The correct cycle is 29 days, 12 hours, 44 minutes, 2.8 seconds.

Reference Numbers and Sizes

  • Ref. 3940: launch 1985, cal. 240 Q, 36mm.
  • Ref. 5140: launch 2006, cal. 240 Q, 37.2mm.
  • Ref. 5327: launch 2008, cal. 240 Q.
  • Ref. 5496: launch 2011, cal. 324 S QR.
  • Ref. 5740/1G: launch 2018, Nautilus case, cal. 240 Q.
  • Ref. 5236P: launch 2021, inline perpetual display, cal. 31-260 PS QL.

Price Bands

  1. $120 to $250: quartz or low-grade automatic, printed moon phase, no leap year.
  2. $300 to $600: Miyota 9015 or Seagull base, moving moon phase, no leap year cam.
  3. $700 to $1,200: modified ETA 2892 or clone, 12mm to 13mm thick, some with working leap year.
  4. Above $1,200: rare. Movement finish still differs from genuine Geneva stripes and beveled bridges.

What Replicas Get Wrong

  • Leap year hand frozen at year 1 or year 4.
  • Month wheel jumps 31 to March on 28-day February.
  • Moon phase disc spins once per 29.5 days, not 29.53.
  • Date font: genuine Patek uses a serif numeral one with a flat top. Replicas use sans-serif.
  • Gold plating wears through in 6 to 12 months on daily wear.
  • Case thickness: genuine 3940 is 9mm. Most replicas measure 11mm to 13mm with a caliper.

Buying Checks

Ask the seller for a video of the date change at midnight. Watch the leap year hand move when you advance four years. Request a caliper photo of the caseback thickness. Request a close-up of the moon phase aperture. Request a photo of the movement under a loupe. If the seller cannot supply these, the watch is a lower tier build.