Liquid fabric softener compositions comprising (a) water-insoluble cationic softeners, (b) water-soluble cationic antibacterial agents and (c) cationic rheology modifying polymers are described that are stable homogenous mixtures. A method for determining stability of the softener formulations or determining the amount of component (a), (b) or (c) involves calculating a stability index of the formulation according to the following equation: Stability formula index=[(wt % of the (a) component+3*(wt % of the (c) component)]/[wt % of the (b) component], wherein a desirable stability index value is 2.5 or greater than 2.5.