Cumulative issue

Cool my dear friend,

1. Cumulative Budget =
CALCULATE(SUM('ExcelBudget'[Budget]), Filter(ALL('Date'), 'Date'[Month] <= MAX('ExcelBudget'[Month])))

Ya , i agree with you it is working great . 

Reason :

Bec it have the continuos month value on ExcelBudget this table am i right ?

2. Cumulative Net =
CALCULATE(SUM('tbFactProspectWon'[NetPrice]), Filter(ALL('Date'), 'Date'[Month] <= MAX('tbFactProspectWon'[DatePaidMonth])))

Reason : 

In this table tbFactProspectWon u don't have continuos value on month am i right ?

Solution :

 Cumulative Net =
CALCULATE(SUM('tbFactProspectWon'[NetPrice]), Filter(ALL('Date'), 'Date'[Month] <= MAX('Date'[Month])))

Try this it will help u.

let me know if it is not solve your problem.