Repeat sum over date range

1.  You need to create a Table with just MONTHS in it to calculate your values per month.  You can do this in Excel and Copy/Paste into PowerBI, or here's code the 'Advanced Editor' code form Query Editor to build a list -100 months back to +100 months foward.  (You can edit the 2nd row as needed.)

let
Source = Table.FromList({-100..100}, each{_}),
AddedStartOfMonth = Table.AddColumn(Source, "StartOfMonth", each Date.StartOfMonth(Date.AddMonths(Date.From(DateTime.LocalNow()),[Column1])), type date),
AddedEndOfMonth = Table.AddColumn(AddedStartOfMonth, "EndOfMonth", each Date.EndOfMonth([StartOfMonth]), type date),
RemovedColumn = Table.RemoveColumns(AddedEndOfMonth,{"Column1"})
in
RemovedColumn

2.  Here is a sample of the Month data & a sample of your table formatting:

3.  Here's the DAX Column code for a column created on the *** Month Table *** that Sums Monthly Savings for each month if the Month Start date falls between your Eff Date & End Date.  

Monthly Savings = CALCULATE(SUM(Table1[Monthly Savings]), FILTER(ALL(Table1), Query1[StartOfMonth] >= Table1[Eff Date] && Query1[StartOfMonth] <= Table1[End Date]))

*** BTW, this assums solid months Start & end Dates.  If this could start/ stop mid-month, you need to create a DAILY table of every day, Create a 'Daily Savings' value in your raw data (DateDiff your two dates + 1 / Monthly Savings, use simular code to find a Daily Savings value, and then SUM up the Days into Months using PowerBI Tables or another DAX Measure.

FOrrest

Hi AdamM,

You may refer to my solution here.

Hope this helps.