The study dealt with how to find the price indices for any base year for a specific time series in the Saudi economy (a model), relying on the price indices for a pre-prepared base year, selected by the Central Bank of Saudi Arabia according to the approved economic and statistical criteria, using some mathematical laws and matrices. And based on the Central Bank of Saudi Arabia data for standard prices at the base year (2013 = 100), the price indices were found at the base year (2007 = 100), and the price indices were found at the base year (2018=100). And by comparing the results that we reached by mathematical methods with the results of the Saudi Central Bank for indices at the base year (2007 = 100) and the price indices in the base year (2018 = 100), the study concluded that the results obtained by mathematical methods match the results approved by the Saudi Central Bank for indices For prices in the two base years (2007 = 100), (2018 = 100) with a slight difference in some years following the base year, which allows researchers to study and discover it later.

Keywords: Base Period, Time Series, Matrix Approach, Price Indices.