The ability to predict properties such as peptide binding and insertion into membranes is an important and time-saving asset in the design of new cell-penetrating peptides (CPPs). Methods to predict those properties are described here, which make use of calculations performed with the Wimley–White hydrophobicity scales. In addition, electrostatic effects can be estimated in a way that provides acceptably close approximations in many cases. Finally, an estimate of the probability of insertion is also discussed. These procedures are illustrated by comparing the calculations with experiments on a few CPPs.