<p>Given the increasing proportion of loblolly pine plantations established with genetically improved material, it is essential to incorporate genetic gains into growth and yield (G&amp;Y) modeling to better reflect genetic influence. This study evaluated the appropriateness of using genetic gain multipliers to incorporate gains into a stand model system (<i>Phase_I</i>), which was originally developed from plantations established with unimproved or low-level improved seed lots in the late 1970s or early 1980s in the western Gulf region. Height gain multipliers were adjusted using age–age genetic correlations to account for the declining nature of relative genetic gain with age. Modeled outputs were then compared with predictions from a more recent stand model (<i>Phase_II</i>), developed from plantations established using improved genetics in the 2000s, as well as with observed genetic gains from two family tests. Results indicated that the gain-multiplier approach, when paired with age–age correlation adjustments, can be effective but tends to overestimate stand volume. While applying the method to integrate gains into G&amp;Y modeling is relatively straightforward technically, the greater challenge lies in obtaining accurate estimates of realized genetic gain from deploying improved material across operational landscapes. This study highlights the importance of establishing realized gain trials; however, in the absence of such data, we recommend reducing estimated gains by 30–40% when applying this method operationally for the species in the region.</p>