<p>This study reports accurate gas-phase homolytic B–Cl bond dissociation energies, obtained using the benchmark-quality W1w thermochemical protocol, for a set of 25 chloroborane-type molecules (known herein as the BCl25BDE dataset). The BDEs of these species differ by as much as 136.6 kJ mol^–1 at 298 K, with (BH₂)₂ BCl having the lowest BDE (388.5 kJ mol^–1 at 298 K) and (CH₃ )HBCl having the highest (525.1 kJ mol^–1). Using the W1w BDEs as reference values, the accuracy of a diverse set of more economical DFT procedures (which may be applied to the study of molecules sufficiently large that the use of benchmark-quality methods such as W1w is rendered computationally prohibitive) have been investigated. As a result of this analysis, the most accurate methods for the computation of B–Cl BDEs are ωB97/A'VQZ (MAD = 3.0 kJ mol^–1) and M06/A'VTZ (MAD = 3.2 kJ mol^–1). The double-hybrid functional DSD-PBEP86 in conjunction with the A'VQZ basis set (MAD = 4.0 kJ mol^–1) was found to give the lowest largest deviation (LD = 6.4 kJ mol^–1) of any of methods considered in this assessment study.</p>