Why January 1st was chosen to mark the start of the year

History · Published 7 October 2026 Swipe more like this →

In short: We celebrate the arrival of the New Year every January 1st, but this date wasn't always the standard. Before the Julian calendar changed everything, the year began in March. Discover how a Roman leader and an Alexandrian astronomer fundamentally restructured time to follow the sun.

The transition to a January 1st start date occurred in 45 B.C. with the implementation of the Julian calendar. Julius Caesar, seeking a more reliable system, worked with the Alexandrian astronomer Sosigenes to move away from lunar cycles. Following the Egyptian model, they opted to track the solar year, calculating it to be 365.25 days long.

To facilitate this shift, Caesar added 67 days to the year 46 B.C., ensuring that 45 B.C. would begin on January 1st instead of in March. He also introduced a leap year mechanism, decreeing that an extra day be added to February every four years to prevent the calendar from drifting out of alignment with the seasons.

However, the system was not perfect. Caesar and Sosigenes estimated the solar year at 365.25 days, failing to account for the more precise value of 365.242199 days. This slight inaccuracy caused the calendar to drift by about 11 minutes each year. By the year 1000, the error had accumulated to seven days, and by the mid-15th century, the discrepancy reached 10 days.

Such shifts meant that January New Year festivities became uncommon throughout the Middle Ages. Even those who strictly followed the Julian calendar did not always observe the New Year on January 1st due to these cumulative mathematical errors. This drift caused significant chronological confusion. Consequently, the celebration of the New Year in January fell out of common practice during the Middle Ages. This period saw various dates used for the start of the year. Even strict followers of the Julian system struggled with the timing.

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