<p>We propose a differential equation for the mathematical description of the kinetics of the isothermal transformation in supercooled austenite. This equation generalizes specific cases, including the Austin–Ricketts and Johnson–Mehl–Avrami–Kolmogorov (JMAK) equations. A series of computational experiments was conducted to evaluate the applicability of the derived equation in describing total transformation kinetics. The findings demonstrate that the generalized equation significantly improves the accuracy of mathematical descriptions for the experimental kinetics of isothermal bainitic transformation.</p>