YOU SAID:
Today is going to be the day I die
INTO JAPANESE
今日は私が死ぬ日になるだろう
BACK INTO ENGLISH
Today will be the day when I will die
INTO JAPANESE
今日は私が死ぬ日です
BACK INTO ENGLISH
Today is the day I will die
INTO JAPANESE
今日は俺が死ぬ日ではない
BACK INTO ENGLISH
Today is not the day I die.
INTO JAPANESE
今日は俺が死ぬ日ではない
BACK INTO ENGLISH
Today is not the day I die.
That didn't even make that much sense in English.