Using formulas to update QTD data

[lj]

Hi, I have a summary spreadsheet that is set up with a QTD budget
column. This column links to a tab that has the budget numbers by
month. Each month when I update the QTD budget column for the new
month I either have to manually update all of the formulas to include
the next month of the quarter, or if it’s a new quarter I have to
adjust all of the formulas to ONLY look at the new month. Is there a
formula or way that I can automate this process, maybe refrencing
dates? Here’s an example of the formula that I’m manually adjusting
each month.

Adjustment at the beginning of the quarter:
From -
=Budget!C31+Budget!D31+Budget!E31


To -
=Budget!D31