How to cumulative sum with condition

This can be accomplished either in a measure to be used in a table,  or in a calculated column in PowerBI's Data View.  The measure, when applied to a table - with the Date column added -  will result in this:

The column added in the Data View will result in this:

Here is the code I used:
Measure

Cumulative Sum = 
VAR current_date = SELECTEDVALUE('Table'[Date])
RETURN

CALCULATE( SUM('Table'[Forecast Value]), 'Table'[Date] <= current_date)
// Returns the sum for all dates less than or equal to the date on the current row.

Column

Running total = 
VAR current_date = 'Table'[Date]
RETURN

CALCULATE( SUM('Table'[Forecast Value]), ALL('Table'), 'Table'[Date] <= current_date)
// Returns the sum for all dates less than or equal to the date on the current row.

Also, If you wanted it to count up differently based on certain criteria - like when it becomes a new year - I would suggest using the column method and doing something like the following:

I hope this helps!  If it does, please mark this as the solution.  Kudos are appreciated 🙂