The International Date Line is between
time zones M(Mike) and Y(Yankee) as imaginary line on the Earth that separates two consecutive calendar days.
Date in the Eastern hemisphere, to the left of the line- time zone M (Mike)- is always one day ahead of the date in the Western hemisphere, to the right of the International Date Line- time zone Y (Yankee).
It has been recognized as a matter of convenience and has no force in international law.