Purpose: Planning ability is one of the core abilities and plays an essential role in problem-solving and decision-makingprocesses. It is mainly critical in childhood to manage school-related demands and carry out daily activities at older ages. Thisstudy aimed to develop and apply a computerized version of the 4-disc Tower of London (TOL) test for planning skills. Design: The research was conducted by three studies, including children, adults, and combined samples. The research consistedof children and adults who were 5-53 years old. Nonparametric tests were used, thereby that the research data had a non normally distributed pattern.Findings: Research results showed significant relationships between age and planning ability, the number of problems solvedon the first trial, and the number of problems solved within three trials. Results showed that increasing planning ability andthe number of problems solved on the first trial was associated with increasing age. The increasing number of problems solvedwithin three trials was associated with decreasing age. There was no significant relationship between age and planning time.Highlights: Research results showed that gender has an effect on planning time in the adult group. Results showed that TOLhas an average medium difficulty level and good item discrimination level in the children sample. Besides, item difficulty anddiscrimination levels of TOL in the adult sample were acceptable. Results showed that the internal consistency level of TOL wasacceptable. In this study, only item difficulty, discrimination, and internal consistency analysis were performed, and studiesincluding detailed validity and reliability analysis can be conducted in future studies.