How Watches Work
Moon Phase Watches Explained: How They Work and Why They're Trending
How a moon phase complication tracks the lunar cycle, how accurate it is, how to set it, and why moon phase watches are one of 2026's fastest-growing trends.
By Brandon Volosov · 4 min read · Updated October 9, 2026
What a moon phase shows
A moon phase display shows the current shape of the moon in the sky, from new moon to full moon and back. A small disc painted with two moons turns slowly behind a window in the dial, so the moon appears to grow and shrink just like the real one.
It's one of the oldest and most romantic complications in watchmaking, and demand is rising: Chrono24 saw moon phase watches grow about 15% in share of demand in 2025.
How accurate is it?
The real lunar cycle lasts about 29.5 days. Most moon phase watches use a 59-tooth wheel that moves one tooth a day, covering two lunar cycles. That's very close, but it drifts by about a day every two and a half to three years.
High-precision versions use extra gearing and can stay accurate for over a hundred years before needing a one-day correction.
Setting your moon phase
- Look up the date of the most recent full moon
- Use the pusher or crown position for the moon phase to advance the disc until the moon is centered (full)
- Then advance one step for each day since that full moon
- Check your watch's manual: many say not to adjust the moon phase or date during certain evening and night hours