This study analyses theoretically the effects of substitutional N on three different chemical vapor deposition diamond growth steps. The investigation is based on density functional theory, using both cluster and periodic models. The reaction steps, assumed to be predominantly occurring during diamond growth, are (i) CH(2) insertion within a carbon dimer, (ii) H transfer from a neighboring surface carbon to an adsorbed CH(2), and (iii) surface migration of CH(2). Carbon atoms at various lateral positions are substituted by N within the second, third, and fourth carbon layers beneath the surface. Both reaction energies and barrier energies were for all reaction steps carefully calculated. For the CH(2) insertion into a carbon dimer, the reaction energy was found to be in principle unaffected by substitutional N. However, the activation energy for the CH(2) insertion reaction was with one exception observed to be significantly increased by the presence of substitutional N. The H migration reaction was only found to be sensitive to the lateral position of N in the carbon layers. The reaction is observed to be favored or disfavored depending on this lateral position. For the CH(2) migration reaction, the substitutional N was observed to increase the activation barriers and thereby negatively affect the reaction kinetics.