For that, you need a separate Date/Calendar table in your model with a 1:M relationship to the Date column in your table. You can then use a measure like this one to get your result. Replact T3Dates and T3 with your Calendar table and original table, respectively.
VAR maxdate =
MAX ( T3Dates[Date] )
LASTNONBLANKVALUE ( T3[Date], SUM ( T3[Amount] ) ),
REMOVEFILTERS ( T3Dates ),
T3Dates[Date] <= maxdate