Mice are increasingly used in studies where measuring insulin sensitivity (IS) is a common procedure. Glucose clamp is labor intensive, cannot be used in large numbers of animals, cannot be repeated in the same mouse and has been questioned as a valid tool for IS in mice; thus, the minimal model with 50min-intravenous glucose (IVGTT) data was adapted in mice. However, specific software and particular ability is needed. Aim of this study was to establish a simple procedure for evaluating IS during IVGTT in mice (CS_I). IVGTT (n=520) were performed in NMRI and C57BL/6J mice (20-25g). After glucose injection (1 g/kg), 7 samples were collected until 50 min for glucose and insulin measurements, analyzed with minimal model which provided the validated reference IS (S_I). By using the regression CS_I=₁+₂xK_G/AUC_D, IS was calculated in 134 control animals randomly selected (regression CS_I vs. S_I: r=0.66, p<0.0001) and yielded ₁=1.93 and ₂=0.24. K_G is the slope of log(glucose_5-20) and AUCD is the mean dynamic area under insulin curve in the IVGTT. By keeping fixed ₁ and ₂, CS_I was validated in 143 control mice (4.7±0.2 min^-1µU^-1ml, virtually identical to S_I: 4.7±0.3, r=0.89, p<0.0001; and in 123 mice in different conditions: transgenic, addition of neuropeptides, incretins, insulin (CS_I: 6.0±0.4 vs. S_I: 6.1±0.4, r=0.94, p<0.0001). In other 120 animals, CS_I revealed its ability to segregate different categories, as S_I does. This easily usable formula for calculating CS_I overcomes many experimental obstacles and may be a simple alternative to more complex procedures when large numbers of mice or repeated experiments in the same animals are required.