the best day in my life VS the best day of my life
Hello ! I'm here to ask about the thing that I mentioned above.
I have studied some movies now, but one of my teacher said "the best day of my life" even though
it sound like "the best day in my life" , the reason she said that like this "the best day of my life" is correct in
grammar. so, I wondered that " the best day in my life" is incorrect? and if there's no error in this, can I use both of them for same situation ?
Thank you in advance!

Question

the best day in my life VS the best day of my life
Hello ! I'm here to ask about the thing that I mentioned above. 
I have studied some movies now, but one of my teacher said "the best day of my life" even though
it sound like "the best day in my life" , the reason she said that like this "the best day of my life" is correct in 
grammar. so, I wondered that " the best day in my life" is incorrect? and if there's no error in this, can I use both of them for same situation ? 
Thank you in advance!

Answer

I wouldn't say that 'best day IN my life" is incorrect - it just isn't natural English.  We say 'best day of my life' 'worst day of my life' - I guess what we are saying is, of all the days of my life - this one is the best.  If you want to speak natural sounding English, stick with 'of'.

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