SUMMARY
An expert system is a computer application designed to help solve a specific problem. The expert system aims to detect early whether the child has deviations from his development by selecting a questionnaire according to the age of the user's baby. The expert system uses the Certainty Factor method. The calculation method to determine the percentage of possible developmental deviations that occur in children uses the Certainty Factor. This study obtained a system accuracy rate of 100% by conducting 75 experiments with experts.