The time-dependent unseparated six delayed neutron group yields are calculated for thermal-neutron fission of 235U. These calculations are based on a recent reference set of delayed neutron precursors, available fission data, and fission systematics. The unseparated calculated time-dependent group yields are compared with separated group yields (groups based on half-life values) and the experimental unseparated group yields. The comparisons indicate the magnitude of the error involved when separated group yields are used for evaluating the accuracy of delayed neutron data. A total delayed neutron yield of 160.62 ± 11.52 per 104 fissions was obtained for thermal-neutron fission of 235U.