N-body simulations show that dark matter haloes develop from theinside out in phases of smooth accretion between major mergers. Inthese conditions it can be shown that the density profile ofellipsoidal anisotropic rotating haloes is completely determined bythe current values of their extensive properties and theircorresponding accretion rates. This allows us to build a simplephysical model for the evolution of the NFW scale radius. Moreover,since we can arbitrarily assume that a halo has grown by pureaccretion, the inside-out growth condition automatically leads to thehalo density profile. We find that the typical accretion ratepredicted by the extended Press-Schechter formalism in any givencosmology leads to a typical density profile of the NFW form for thecorrect mass-concentration relation.