The KATRIN experiment can perform a comparably low-statistics search for keV-scale sterile neutrinos with the first tritium measurements, improving the current laboratory limits on the squared sterile-to-active mixing angle by about one order of magnitude. For the keV-scale sterile neutrino search a wider energy range of tritium β-decay spectrum has to be measured, as the “postulated” neutrinos would manifest themselves as a kink in the spectrum at an a priori unknown energy. For this reason a precise model of the entire spectrum is necessary. In this poster we present a novel technique to simulate the full spectrum, taking into account experimental effect appearing in KATRIN-like experiments. The model is constructed from the responses of each individual experimental component: the tritium source, the spectrometer and the detector. The influence of systematic uncertainties is discussed.