Synthesis of NdFe<SUB>12</SUB>N film by Hirayama et al.  has attracted renewed interest in the ThMn<SUB>12</SUB>-type compounds. Although NdFe<SUB>12</SUB>N has large saturation magnetization and reasonably strong magnetocrystalline anisotropy , its thermodynamic instability prevents industrial applications. We have performed density functional calculations of NdFe<SUB>11</SUB><I>M</I> for <I>M</I>=Ti, V, Cr, Mn, Co, Ni, Cu, Zn. We found that Co can contribute to phase stability, and NdFe<SUB>11</SUB>CoN has large saturation magnetization and crystal-field parameter <I>A</I><SUB>2</SUB><SUP>0</SUP> comparable to NdFe<SUB>12</SUB>N. We also found that the magnetic exchange coupling between Nd and Fe has a big impact on magnetic anisotropy at high temperatures, and the strength of the coupling varies significantly by interstitial nitrogenation.  Y. Hirayama et al., Scripta Materialia 95, 70 (2015).  T. Miyake et al., J. Phys. Soc. Jpn. 83, 043702 (2014).