Context : It was recently demonstrated that the eruption of V1309 Sco was a result of a merger of the components of a cool contact binary .

Aims : We computed a set of evolutionary models of the detached binaries with different initial parameters to compare it with pre-burst observations of V1309 Sco .

Methods : The models are based on our recently developed evolutionary model of the formation of cool contact binaries .

Results : The best agreement with observations was obtained for binaries with initial masses of 1.8-2.0 M _ { \sun } and initial periods of 2.5-3.1 d. The evolution of these binaries consists of three phases : at first the binary is detached and both components lose mass and angular momentum through a magnetized wind .
This takes almost two thirds of the total evolutionary lifetime .
The remaining third is spent in a semi-detached configuration of the Algol-type , following the Roche-lobe overflow by the initially more massive component .
When the other component leaves the main sequence and moves toward the giant branch , a contact configuration is formed for a short time , followed by the coalescence of both components .

Conclusions :