Since the solar calendar is used in Japan now and the Japanese calendar corresponds to the Christian calendar, the method of counting a person's age in the traditional Japanese system will be as follows: 'traditional Japanese system = your age + two' as for the period from the New Year's Day until the day before birthday, and the 'traditional Japanese system = your age + one' from your birthday and afterwards.
日本では現在は太陽暦を用いており、和暦と西暦の日付は一致するので、自分の今年の数え年は、元日から誕生日前日満了までは「数え年＝満年齢+2」、誕生日前日満了以降は、「数え年＝満年齢+1」で計算する。