[General] Did not see or have not seen?

[kopiteste]

I have just had a converstaion with a colleague in which she said "I did not see him today." I told her the correct way would be to say "I have not seen him." Can anyone explain to me why this is the case?

 

[5jj]

I have just had a converstaion with a colleague in which she said "I did not see him today." I told her the correct way would be to say "I have not seen him." Can anyone explain to me why this is the case?

Both can be correct.

We would be more likely to use the past simple later in the day, for example after the working day has finished.

We would be more likely to use the present perfect if there is still some chance that we may see him today.