Let b > 1 be a positive integer, we prove a criterion for complexity in g-ary expansions of rational fractions. We prove that for any purely periodic proper fraction a/b and all j ≥ 1, each sequence of j digits occurs in the g-ary repetend of a/b k with relative frequency that approaches 1/g j for increasing k. The absolute frequencies can be calculated by means of a simple transition matrix. Let (a k ) be a sequence of positive integers relatively prime to b. We prove that each sequence of j digits occurs in the g-ary repetend of a k /b k with a relative frequency that approaches 1/g j for increasing k unless all prime factors of b divide the base g ≥ 2.