This work presents a probabilistic interval analysis method for the tolerance analysis of discrete and continuous apertures. Given the knowledge of the interval tolerances, and starting from inclusive pattern bounds obtained using state-of-art interval analysis tools, a novel methodology is here introduced that allows to compute, in closed-form, the probability distribution of the random pattern occurrences within the interval bounds. A numerical example is reported showing the advantage of the proposed approach with respect to the state-of-art interval analysis methods.