In the perspective of the busy life schedule in the modern society, the accepted minimum period of sexual cohabitation resulting in no offspring for a couple to be declared infeile is:
90% of couple who are cohabiting for at least one year with out contraception will have a conception. This is on monthly conception rates of 20 - 25 % in normal young couples attempting pregnancy.
One year
One and a half-year
Two years
Three year
Infeility (Eggs'plantation!)