Including Leap Year in Calculaton

Project TimeLineI have a project time line which uses a calendar, the calendar places markers of due dates for each milestone (see attached link). When looking at February 2016, it is not taking into consideration that the month in that year is a leap year; what calculation can I include with my existing calculation to include a leap year?

My calculation:

=IF(IF(DAY(EOMONTH(DATE(YEAR,MONTH($N$18),1),0))>IF(S23>=1,S23,IF(VLOOKUP(T$19,Sheet2!$E$2:$F$8,2,FALSE)=WEEKDAY(DATE(YEAR,MONTH($N$18),1)),1,0)),IF(S23>=1,S23+1,IF(VLOOKUP(T$19,Sheet2!$E$2:$F$8,2,FALSE)=WEEKDAY(DATE(YEAR,MONTH($N$18),1)),1,0)),0)<T22,0,IF(DAY(EOMONTH(DATE(YEAR,MONTH($N$18),1),0))>IF(S23>=1,S23,IF(VLOOKUP(T$19,Sheet2!$E$2:$F$8,2,FALSE)=WEEKDAY(DATE(YEAR,MONTH($N$18),1)),1,0)),IF(S23>=1,S23+1,IF(VLOOKUP(T$19,Sheet2!$E$2:$F$8,2,FALSE)=WEEKDAY(DATE(YEAR,MONTH($N$18),1)),1,0)),0))