There is no shortage of methods available to compute the values you are looking for in Tableau. The route to use depends on the display and interaction you want to allow for.
Attached is an example using a nested table calculation, and the difference between the annual and quarter sheet is just a pill.
If you want to display all numbers on the same sheet or you want to use the subtotals area to display the totals, that is possible as well.
There are lots of options, the attached is just a starting point.
wt_avg-_example_jm_edit.twbx 24.9 KB
Joe, thank you so much for your response.
Is there no solution that way to utilize the functionality of the Date field? Also, the solution you provide doesn't seem to show the correct figures when the Sub-Totals or Grand Totals are turned on.
Any suggestions/alternatives would be greatly appreciated!