The use of the Present Perfect is often because there is information (often implied and unstated) about the present. The Past Simple describes finished time (not necessarily finished actions) [Eg I was at home yesterday and I am at home today]. Anyways... consider this scenario - similar to your question: Teacher "Class, have you done your homework? Because I want to talk about it now" Teacher "Class, did you do your homework? Good. Today I want to..." [Main source: M. Lewis "The English Verb"] So, as others have stated both are possible. It is important to remember that in English it is not the action that determines the tense, but the message the speaker wants to communicate.

'Have' has two functions here. 1) for emphasis. I.e. Didn't you finish? I HAVE finished! 2) British English Did you see my keys (US) Have you seen my keys? (UK)

Hello! Both are possible and I can't see any difference in meaning. Perhaps I have done the work today suggests you have done it more recently than I did the work today, but that's all I can think of.

Both are completely fine. There is only a very slight difference in meaning, since the time period in both is "today" - which is very recent. "I did", the simple past, is the straightforward and obvious choice, and it turns out that in English the simple past is the most-used past tense. This is probably the one you want. But the other choice is not wrong. "I've done", which is contracted from "I have done", is the present perfect tense - which is also well used. Often we use it when there is a sense that what happened (in the past) has significance in the present, or because the activity started in the past and continues into the present. It's also often used to make announcements, which could apply in your example if this is in some kind of conversation or message exchange. The link at the bottom includes this about the present perfect : "This is common when we want to introduce news and we often use the words 'just / yet / already / recently'. However, the past simple is also correct in these cases, especially in US English. " https://www.perfect-english-grammar.com/present-perfect-use.html https://ginsengenglish.com/blog/english-verb-tense-frequency