Help needed with DAX...Please help....

Calendar must be a date table in the model that's been marked as such in order for the formula to work.

// Your model should be a star-schema with
// conformed dimensions. If it's not, then
// the DAX will always have problems of some
// sort. Please create correct models to
// avoid mistakes. Google for "star schema
// in Power BI" to learn about what a good
// model is.

// Assuming that Calendar is connected to
// both tables on the corresponding date fields
// and the relationships are one-to-many with
// one-way filtering.

[Total Left] =
var vLastVisibleDate = MAX( 'Calendar'[Date] )
var vLastVisibleQty =
    CALCULATE(
        SUM( 'Inventory Table'[Quantity] )
         - SUM( 'Receivor Table'[Quantity] ),
        Calendar[Date] <= vLastVisibleDate
    )
RETURN
    vLastVisibleQty