An in-depth discussion of the problems of the current description of the growth rate (or doubling time) of breeder reactor fuel emphasizes the need for conceptually improved computational procedures. The presented derivation of improved measures for the growth of breeder reactor fuel is based on a formally correct description of the fast reactor fuel cycle. From these derivations one obtains a hierarchy of four logically different expressions for the fuel growth rate, which yield formally the same value. The first (and most general) definition is obtained by mathematically expressing the doubling time as a measure of the asymptotically exponential growth of fuel in a system of identical breeder reactors. The second definition represents the condensation of the detailed information of the equilibrium fuel cycle analysis for a single reactor. The third growth rate expression is also based on the detailed fuel cycle analysis. Coefficients of an“integrated fuel cycle model” are obtained from the detailed information. This leads to an eigenvalue problem with the growth rate as eigenvalue and the equilibrium plutonium composition as eigenvector. The fourth growth rate expression is based on a set of isotopic weight factors, which is obtained as solution of the adjoint of the fuel cycle eigenvalue problem employed in the third procedure. The resulting “breeding worth factors” are applied to the production and consumption rates of the four plutonium isotopes. This makes the resulting doubling time formula stationary with respect to variations about a reference reactor and practically independent of the fuel composition.