» Summing Annual Expenses by Respective Quarters

Problem:

The range A2:B9 contains a list of dates with corresponding expenses.
We want to create a total of the expenses paid during each quarter.

Solution:

Use the SUM, ROUNDUP, and MONTH functions as shown in the following Array formula:
{=SUM((C2=ROUNDUP(MONTH($A$2:$A$9)/3,0))*$B$2:$B$9)}

Screenshot // Summing Annual Expenses by Respective Quarters