Perpetual vs Annual Calendar

Annual calendar

• Knows months have 30 or 31 days.
• Needs manual adjustment once a year at the end of February.
• Patek Philippe invented the modern version in 1996 (Ref. 5035).

Perpetual calendar

• Knows months and leap years.
• Needs manual adjustment in 2100 (when the Gregorian leap-year rule skips).
• Mechanism: 48-month cam that accounts for Feb 28/29.

Why the gap matters

Annual calendars use ~150 fewer parts than perpetuals. Pricing reflects it — an entry-level annual (IWC, JLC) costs ~₹8L; an entry perpetual (Frédérique Constant, Lange) starts at ~₹15L.