I currently have a header and on that header there is a plus button with three options, one of them being add expenses. On the expenses page of my app, I can't decide whether there should be a second "add new" button or if I should only have the one option in the header. The header button will always be available on every screen, but requires two clicks while the "add new" is only available on the expenses but only requires one click. Here is the wireframe.
I don't think the problem is in the repetition, the redundancy in UX is not a serious issue. As for the UI, I think the biggest drawback is the proximity, one below the other, which in terms of page layout or structuring goes from redundant to obvious.
If the user already knows the + button can add an expense because they have already navigated through other screens of the application, on the expense screen there may be a fixed reminder button Add new in the place the new expense will occupy.
To me, the + doesn't tell me what I expect to happen. If you hadn't explained it, I would be guessing. Therefore, I would never click it. The plus should go next to expenses, because that is what you are adding.
For that matter, "Add New" What? Might sound obvious, but it could add a new category. Why not [ Add Expense ] There is room and it tells you EXACTLY what it does.
One other question: When you add, what order does it add them in? Does it depend on the sort? Let's say it is sorted desc, you click [ Add new ] and it goes to the top. Not that intuitive. Even worse, what if you are adding expense 21 and it is sorted Desc, you have to scroll to the top to see the newly added expense.