Which calendar's New Year's Eve is celebrated with the Hogmanay tradition in Scotland?

Scotland's Hogmanay New Year's Eve is celebrated according to the Gregorian calendar.

Hogmanay is the Scottish celebration of the New Year that begins on January 1 in the Gregorian calendar. Its public events take place on December 31 and around midnight, when the calendar year changes. Scotland adopted the Gregorian calendar in 1600, earlier than many parts of Great Britain, which adopted it in 1752.

The Gregorian calendar was introduced by Pope Gregory XIII in 1582 as a reform of the Julian calendar. It adjusted the leap-year rule to keep calendar dates better aligned with the seasons. Hogmanay's customs are Scottish, but the date of the modern celebration follows the same civil calendar used in most countries. This distinguishes it from New Year festivals based on lunar or lunisolar calendars.