Disclosed is a method of tailoring infant formulas to individual nutrition needs prior to use. The method comprises (A) determining the desired volume and optimal caloric density of a formula to be fed to a preterm or low birth weight infant; (B) obtaining a plurality of base infant formulas, all in liquid form, comprising fat, protein, carbohydrate, vitamins, and minerals, each of which has an osmolality of from about 200 to about 360 mOsm/kg water and a different caloric density within a range of from about 609 to about 1082 kcal/L; (C) selecting two of the base liquid formulas having a caloric density value above and below the optimal caloric density, (D) calculating the volume of each selected base formula needed to produce the desired volume of an infant formula blend having the optimal caloric density; (E) combining the calculated volumes to produce a an isotonic blend having the desired feeding volume and optimal caloric density, The formula is then fed to the preterm or low birth weight infant. Also disclosed is a hypercaloric infant formula suitable for use in the disclosed method, and infant formula kits comprising the plurality of base formulas and a device (e.g. calculator, computer program, chart with precalcuated blend volumes) for calculating blend volumes.