Real, published equations -- not a fabricated or ML-based prediction. These are the standard Fick's First Law (steady-state permeation flux) and Higuchi (1961/1963) matrix-release models used throughout pharmaceutical sciences. Diffusion (D) and partition (K) coefficients must come from real experimental data (e.g. Franz diffusion cell studies) or a validated estimation method -- this tool does not invent per-drug values. Where no experimental D/K is available, a rough QSPR estimate (Potts & Guy, 1992) is offered, clearly labeled as an approximation. Confirm with real in vitro permeation/release testing before any formulation or regulatory decision. See also Complex Generics & 505(b)(2) Pathway Planner.