[en] This work will focus on the correct usage and validation of the MCNP KOPTS, kinetics options, card to obtain Rossi-a, or prompt neutron decay constant, for a system. The validation will focus on recent prompt neutron decay constant measurements completed at the National Criticality Experiments Research Center (NCERC) with comparison to both benchmark level and best working MCNP input decks. Measurements performed on Polyethylene Class Foils, HEU Zeus, HEU/Pb Zeus, IEU/Pb Zeus, KRUSTY, and Jupiter will be compared to their respective calculations. The prompt neutron decay constant measurements cover an energy spectrum of fast to thermal and two major fissionable isotopes, Uranium-235 and Plutonium-239, with different reflectors and interstitial materials. For each of these experiments, prompt neutron decay constant measurements are performed on several subcritical configurations. The Rossi-a, or prompt neutron decay constant at delayed critical, is always extrapolated from subcritical measurements, but in some cases direct measurements of the prompt neutron decay constant are taken at delayed critical. For the simulations performed in this work, the best available input deck is used to calculate the value of the prompt neutron decay constant at delayed critical. This paper will stress the importance of closely matching the critical configuration of the experiment when obtaining a result from the KOPTS card. This is due to the method in which the code calculates the prompt neutron decay constant. An explanation of this methodology is included. Based on the results included in this work, the KOPTS card in MCNP has a tendency to over-predict the prompt neutron decay constant by about 10 %. (author)