Treating the standard model as an effective field with three weakly interacting neutrinos at energy below the center-of-mass energy of an experiment, neutrino mass arises from the dimension-5 Weinberg operator. The neutrino kinetic term can be further modified due to dimension-6 operator. In this case, the lepton mixing matrix U is no longer unitary and results in nonorthogonal flavor states. Since the flavor state space is complete, in an experiment, the probabilities that a neutrino of a certain flavor being detected as all possible flavors should sum to unity. Using the naive Born rule with nonunitary U, the total probability can be larger or smaller than unity. It is the aim of this talk to show how one can calculate the oscillation probabilities such that the total is always unity.