Bandgap energy of dilute nitride GaInNAsSb/GaAs alloys with N compositions as high as 8% are estimated using a method based on band anti-crossing model used for GaNAs/GaNSb/InNAs/InNSb ternary compounds. The parametrization of the model is defined by fitting with experimental composition and bandgap energy values employing a differential evolution algorithm. The effects of lattice strain on the bandgap energy are taken into account by the model resulting in an accurate prediction of the bandgap energy with an average deviation of only 12 meV compared to the experimental data. The model provides a useful tool for accurate determination of bandgap energies of dilute nitrides, including narrow bandgap, i.e. ∼0.7 eV GaInNAsSb alloys, which are becoming increasingly relevant in the development of high-efficiency lattice-matched multijunction solar cells. Peer reviewed