We develop a numerical and an analytical approach to estimate the persistence length lp and mean-square end-to-end distance 〈R2〉 of complex semiflexible polymers. Numerically, lp and 〈R2〉 are determined by averaging a large set of single chain conformations with the correct dihedral angle distributions p(φi). Analytically, lp and 〈R2〉 are extracted from the tangent-tangent correlation function. We apply both approaches to two semiflexible conjugated polymers, poly(3-hexylthiophene) (P3HT) and poly((9, 9-dioctyl-fluorene)-2, 7-diyl-alt-[4, 7-bis(thiophen-5-yl)-2, 1, 3-benzothiadiazole]-2′,2′-diyl) (PFTBT). Results obtained via the two methods agree for polymers with any degree of polymerization N. Our methods can be applied to any semiflexible polymers with any number of distinct moieties.