SUMGT calculated KF

hi,
I have created a CKF1 which is checking if the enddate > 60 days than the begindate. CKF1 = GT("Enddate",MAX("Begindate",60))
Now I am trying to SUMM up a revenue field based on the CKF1 field. If the result = 1 it should SUM the revenue otherwise not. I tried something like this SUMCT("Revenue") EQ ("CKF1",0)) but the syntax is not right. Is this possible? if so what should be the syntax?
any help is appreciated.
br, Ralph