In this paper, we present a GIAO-HDFT universal scaling factor and a linear regression comparative study, in which we intent to investigate the ability of GIAO-mPW1PW91/6-31G(d) using optimized geometries at the PM7 level of theory to achieve its high cost-effectiveness ratio. This level is computationallymuch less demanding than GIAO-B3PW91/cc-pVDZ//B3PW91/cc-pVDZ and GIAO-B3PW91/cc-pVTZ//B3PW91/cc-pVDZ, recently published for our research group. Despite the calculation approximations the chemical shifts calculated at the GIAO-mPW1PW91/6-31G(d)//PM7 using a simple relationship (λscal = 1.06. λcalc -0.72, where λcalc and λscal are the calculated and the linearly scaled values of the 13C chemical shifts, respectively) were able to yield MAD and RMS errors as small as those obtained with other GIAO-HDFT (B3LYP, OPBE, B3PW91) with bigger basis sets, such as 6-311+G(2d,p) and cc-pVDZ and cc-pVTZ. Its high cost-effectiveness ratio scaling factor, as well as its successful applicability to practical problem, was confirmed. In conclusion, GIAO-mPW1PW91/6-31G(d)//PM7 linear regression obtained by using the experimental and the calculated data, is a very attractive tool as an alternative to more computationally demanding approaches, which are usually applied in order to achieve 13C NMR chemical shift calculations.