The performance of different DFT functionals (B3LYP, BHLYP, CAM-B3LYP, MO6HF) on the prediction of vertical transition energies E-vert of low bandgap homopolymers is tested against the experimentally available oligomer series (thienopyrazines and thienothiophenes). This allows for a detailed and accurate comparison on the consistency of DFT methods for chainlength evolution and polymer limit prediction, and for an understanding of geometry and time-dependent contributions to E-vert by combinatorial analysis. Together with former studies on wide/medium bandgap polymers and low bandgap co-polymers, our results on low bandgap homopolymers suggest offset-corrected MO6HF as the most viable method for time inexpensive and reliable prediction of semiconducting polymers at the moment. (C) 2016 Elsevier B.V. All rights reserved.