Since I download information in an excel database everymorning, is there any way I can link each new table with the old table and perform an automatch that matches each liked amounts and returns the value of the difference in one field?

You can create a query to join the old and new tables.

Select t1.fldA, t1.fldb, t1.AmtFld - t2.AmtFld
From t1 inner join t2 on t1.fldA = t2.fldA and t1.fldB = t2.fldB
Where t1.AmtFld - t2.AmtFld <> 0;