Cumulative addition on montlly P & L sheet

Based on your version and suspected layout where we assume A1 says Jan Budget, B1 says Jan Actual etc and row 2 contains values where Budget is added in advance and Actuals as created...

YTD Budget
Y2:
=SUMIFS($B2:$X2,$B$1:$X$1,"*Budget",$A2:$W2,">-9.99E+307")

YTD Actual
Z2:
=SUMIF($A$1:$W$1,"*Actual",$A2:$W2)

To clarify above...
Budget YTD sums all values where header says "something Budget" and where there exists an accompanying Actual value.
Actual YTD sums all values where header says "something Actual"

My mistake - I reversed the range references incorrectly... based on budget, actual, budget, actual etc... with Jan Budget being A1

YTD Budget
Y2:
=SUMIFS($A2:$W2,$A$1:$W$1,"*Budget",$B2:$X2,">-9.99E+307")

YTD Actual
Z2:
=SUMIF($B$1:$X$1,"*Actual",$B2:$X2)

You have a trailing space after Budget (ie "Budget ") so either:

=SUMIFS($C3:$Y3,$C$2:$Y$2,"Budget*",$D3:$Z3,">-9.99E+307")

else, remove both trailing space from headers and wildcard from SUMIFS

=SUMIFS($C3:$Y3,$C$2:$Y$2,"Budget",$D3:$Z3,">-9.99E+307")