Dipolar magnetic field strength as a function of apparent V-band magnitude for the magnetic massive stars. The dashed line indicates our estimated empirical detection threshold. Open triangles indicate lower limits on B_d; red symbols show the position of the stars having a fractional MS age smaller than 0.5. Arrows point to the B_d values that young stars (i.e., τ< 0.5) would have on the TAMS assuming flux conservation.