We define a complexity measure on context-free grammars called end. Roughly speaking, for a context-free grammar G, endG(n) measures the distance of variables from the ends of sentential forms along the derivations of words in L(G) of length n. We prove in a constructive way the regularity of L(G) whenever endG(n) is constant. Yet, we improve on this by showing that if L(G) is nonregular then endG(n) = Ω∞(log n). Finally, the optimality of such a lower bound is established.