Simple analytical formulas for prompt estimation of the yield and angular distribution of neutrons for calculating the biological shielding of heavy ion accelerators with energies from 1 to 6 MeV/u are presented. The results of calculation are compared with those obtained with the help of the programs LIZE++ and FLUKA as well as with the experimental data available in literature. On the basis of the comparison it can be said that the proposed method can be applied for prompt estimation of the required biological shielding for heavy ion accelerators with energies from 1 to 6 MeV/u that are being constructed or reconstructed. The deviation of the results of such calculations from more precise ones does not exceed a factor of 2, which is comparable with deviations in calculation of biological shielding due to some variety in the spectra of the produced neutrons and variations in protective properties of the materials used as well as in their thickness.