You can colour a cell to meet your condition with conditional formatting, then use a sum formula to calculate the sum to that point.


eg.


Assuming your table is in A1:AF13 and you enter a date in, say, cell A17.


Then you would select cell A1 and go to Home|Condional Formatting|New Rule.
Select "use a formula...." and enter formula:


=ADDRESS(ROW(),COLUMN())=ADDRESS(MATCH(TEXT($A$17, "mmm"),$A$1:$A$13,0),MATCH(DAY($A$17),$A$1:$AF$1,0 ))


Click "Format" and choose from the "Fill" tab. Keep clicking "OK" until finished. You should see a cell coloured corresponding to date in A17.


Now to sum use formula:


=SUM(OFFSET($A$1,MATCH(TEXT(A17,"mmm"),$A$1:$A$13, 0)-1,1,1,MATCH(DAY(A17),$A$1:$AF$1,0)-2))