We sought to calculate the extra social costs resulting from child abuse in residential care facilities (RCFs) for children with disabilities (CWD) in Japan. We distributed a survey to 260 residential facilities for CWD in 2020 and obtained responses from 91 facilities. Among the children admitted to these facilities, 23–67% were affected by child abuse. We estimated the extra costs to be an average of USD 647.7 million. This study is meaningful in that there are no existing official statistics or research findings on the extra costs of residential care due to child abuse in Japan.