We computed the vertical ionization energies at the geometry of the neutral ozone using a composite method. The starting value is the complete basis set (CBS) extrapolation of the EOM-IP-CCSDT/cc-pCVnZ energies with n = 5, 6. These values were augmented with two corrections: the ∆Q (quadrupoles) correction in the cc-pwCVTZ basis set and the relativistic correction calculated using EOM-IP-CCSD/cc-pwCVTZ. The error bars were estimated as follows: for the extrapolated CBS reference values, we used half of the absolute value of the difference between the best ab initio value and the extrapolated value, and for the remaining corrections (quadruples correction, ∆Q, and the relativistic correction) we used half of the absolute value of the correction.