The longitudinal actor-partner interdependence modeling framework (L-APIM) is often used to study actor and partner effects in dyadic intensive longitudinal data. To capture curvilinear actor and partner patterns, the L-APIM can be extended to include quadratic actor and partner effects. A burning question is how to conduct power analyses for different L-APIM variants. In this paper, we introduce a power analysis application, called PowerLAPIM, and provide a hands-on tutorial for conducting simulation-based power analyses for 32 L-APIM variants, many of which include quadratic effects. With PowerLAPIM, we target the number of dyads needed, but not the number of repeated measurements for both partners, because this is usually fixed in many longitudinal dyadic studies. PowerLAPIM allows studying moderation of the linear and quadratic actor and partner effects by incorporating time-varying covariates or a categorical dyad-level predictor to test group differences. We also provide the functionality to account for serial dependency in the outcome variable by including autoregressive effects. We illustrate how to perform a power analysis for a longitudinal dyadic study using PowerLAPIM based on data from 94 heterosexual couples for which both partners simultaneously reported on their feelings and experiences several times a day for one week.