They are both correct. You would use sentence 1 in the middle of the day. It suggests that the day has been good so far and you expect that it will continue to be good. Sentence 2 would be used at the end of the day. I would disagree with David K. about 'It was a good day' sounding more natural. Both sentences are correct but in my experience speakers of British English are likely to use the present perfect and speakers of American English the past simple.

If the day is over, #2 is correct. An alternative “Today was a good day” has a very similar meaning and is more natural.

Hi Agnieszka In fact both are grammatically correct. You have a point about question 2 because technically you are talking about past events connected to the present. And a good day could change at any moment and become a bad day at any point before that day is finished...so stating "it is a good day" as a fact that can't change is a bit wrong. Saying "it has been a good day" (so far) is more accurate. However, it's worth noting that people do use the present tense to talk about this type of thing - and they don't really think too much about the possibility that things might change. Often people decide to say "it has been a good day" to do one of two things: 1. signal/imply that they are in a good mood now because of things that happened in the past or 2. to suggest that things are about to change Hope this helps Chris