Which calendar marks New Year's Day on January 14 in some Orthodox Christian traditions?

The Julian calendar marks New Year's Day on January 14 when its date is compared with the modern Gregorian calendar.

Some Orthodox Christian communities and countries observe an “Old New Year” according to the Julian calendar. In the 20th and 21st centuries, January 1 in the Julian calendar falls on January 14 in the Gregorian calendar because the calendars differ by 13 days. The date difference will change in 2100 when the gap becomes 14 days.

The Julian calendar was introduced by Julius Caesar in 46 BCE and took effect in 45 BCE. Its leap-year rule was slightly too long, causing the calendar to drift relative to the solar year. Pope Gregory XIII's reform in 1582 produced the Gregorian calendar used internationally today.

Old New Year is observed socially or religiously in places including parts of Eastern Europe and the Balkans, but practices vary. It is not a separate astronomical New Year; it is a calendar-date distinction.