Google how did we decide on picking january 1st as the first day of the year

In designing his new calendar, Caesar enlisted the aid of Sosigenes, an Alexandrian astronomer, who advised him to do away with the lunar cycle entirely and follow the solar year, as did the Egyptians. The year was calculated to be 365 and 1/4 days, and Caesar added 67 days to 45 B.C., making 46 B.C. begin on January 1, rather than in March.

Idon’t understand your question but if u mean the difference in america vs in africa