Your question is not completely clear to me. You can add any field to your table. It is, however, always much better not to add any field for a value which can be calculated, based on values in other fields. By including such a field the chance to get an inconsistency will grow.
In a query it is always possible to add a field based on a calculation. Suppose you have a field EntryDate and you want to show a date 90 days later add to the query grid the following text.
DueDate: [EntryDate] + 90
You can base a report on a query. If you use the report wizard it will often go well, as long as you do not have too many fields.
Only if you have more experience, do it different. My advice is always when starting with Access: try to design in the query builder a query which will give you the fields [included calculated fields] you want. The query is becoming too complicated? No problem, do it step by step. Make for instance a query based on two tables. Use that to add a third table. Itis often a safe way to avoid problems with ambiguous joins. Perhaps a grouping is needed? That could be the next step.
This is not the desired end situation. However, for checking if it all works and as long as your database is not too big, why making all the fuss to optimize and show how complicated you can make it with VBA code?
Perhaps clarify a little bit what you need exactly before rejecting all answers. You can always decide at a later moment if the answers were of any help. 100% you will hardly ever get for free.
Good luck
