The select into will auto generate your temp table.
either you remove the create table of the temp table or you remove the into part of the select and add an insert into
DROP TABLE #OutPutTBL
SELECT SUM(CONVERT(INT, TargetDate)) AS TargetDate, SUM(CONVERT(INT, ActualDate)) AS ActualDate, SUM(CONVERT(INT, CompleteRate))/SUM(CONVERT(INT, TargetDate)) AS CompletePercentage, Months
into #OutPutTBL
FROM #FORMULA
GROUP BY Months
SELECT* FROM #OutPutTBL
or remove the select into
DROP TABLE #OutPutTBL
CREATE TABLE #OutPutTBL(TARGETDATE INT, ACTUALDATE INT, PERCENTAGE INT, MONTH VARCHAR(5))
insert into #OutPutTBL
SELECT SUM(CONVERT(INT, TargetDate)) AS TargetDate, SUM(CONVERT(INT, ActualDate)) AS ActualDate, SUM(CONVERT(INT, CompleteRate))/SUM(CONVERT(INT, TargetDate)) AS CompletePercentage, Months
FROM #FORMULA
GROUP BY Months
SELECT* FROM #OutPutTBL