The Leap 42 Calendar

Leap 42 proposes a parsimonious decimal calendar and timekeeping architecture designed to minimize structural irregularity in civil temporal systems. The model combines decimal time—10 hours per day, 100 minutes per hour, and 100 seconds per minute—with a ten-month calendar consisting of nine uniform 36-day months and a terminal balancing month containing 41 days in standard years and 42 days in leap years. Unlike prior decimal calendar proposals that externalize remainder days as intercalary festival periods, Leap 42 localizes all irregularity inside a single terminal month while preserving continuous calendrical identity for every date. Anchoring the year start to the winter solstice preserves calendar integrity over the span of millennia. The paper formalizes the calendar geometry, leap semantics, ordinal arithmetic, absolute day numbering, timestamp algebra, serialization rules, Gregorian interoperability, Unix/SI conversion semantics, and derived computational properties. It frames the system as a piecewise-regular temporal architecture optimized for software simplicity, deterministic arithmetic, machine-native scheduling, archival systems, distributed ledgers, simulation environments, and computational governance contexts. Rather than advocating immediate civil replacement of Gregorian timekeeping, the work explores how temporal systems can be redesigned under principles of bounded irregularity, decimal coherence, and computational parsimony.