The ARIMA model can analyze univariate data (describing data simply to find patterns within the data) that contains seasonal patterns and trends. The application of the ARIMA algorithm to automatically predict the auction prices of used cars at the Balai Lelang Mobil Medan, designing and building a web-based car auction price prediction application. Data collection for the research was conducted at the Balai Lelang Mobil Medan, and data processing was carried out at the University of Islam Sumatera Utara. The results of the research indicate that the Used Car Auction Price Prediction Application at the Balai Lelang Mobil Medan, utilizing the ARIMA algorithm, can be accessed by administrators and potential buyers, where potential buyers can predict used car auction prices based on the dataset entered by the administrator.