Global waste accumulation necessitates sustainable pavement solutions. This study focuses on sustainable pavements by adopting the waste-to-wealth approach using waste cooking oil (WCO) as rejuvenator to incorporate higher reclaimed asphalt pavement (RAP). A novel approach optimises WCO for recycled mixtures with different field RAP contents. The optimum WCO was assessed for mixtures with laboratory-aged RAP, considering binder performance, properties of laboratory-aged RAP binder, and moisture susceptibility. Optimum dosages were then determined for the mixtures with field RAP without compromising moisture susceptibility. These dosages depend on the percentage and viscosity of the extracted binder of field RAP. Results indicated that the recycled mixture with field RAP and corresponding optimum WCO assessed from the proposed method exhibited satisfactory moisture susceptibility unlike the recycled mixtures without WCO. Also, the method suggested a way to estimate the total optimum binder content, if higher RAP is being used considering the inactive binder of RAP.