Moon Phase Watch Calculator
Calculate the current moon phase, check your moon phase watch accuracy, and determine correction schedules for your timepiece.
Current Moon Phase Calculator
Calculate the current moon phase for setting your moon phase watch.
Moon Phase Accuracy Calculator
Calculate how accurate your moon phase watch mechanism is over time.
Correction Schedule
Calculate when your moon phase watch will need its next correction.
Formula
Frequently Asked Questions
How accurate is a moon phase watch?
How do I set the moon phase on my watch?
When does a standard moon phase need correction?
Understanding Moon Phase Watches
The moon phase is one of the oldest and most romantic watch complications, dating back to the earliest pocket watches. It displays the current phase of the moon through an aperture on the dial, using a disc with two painted moons that rotates behind a shaped opening.
How Moon Phase Mechanisms Work
The moon disc has 59 teeth (representing two lunation cycles of 29.5 days each). A finger advances the disc by one tooth every 24 hours. The true synodic month is 29.53059 days, so the 29.5-day approximation creates a small but cumulative error.
Precision Levels
Standard (59-tooth): 1 day error per 2 years 7 months. Found in most moon phase watches.
High Precision (135-tooth): 1 day error per 122 years. Found in A. Lange & Sohne and IWC.
Astronomical: 1 day error per 1,000-5,000+ years. Found in Patek Philippe and some independent watchmakers.