Solar radiation on a region is one of the main parameters in deciding on the economy of conversion devices designed to utilize solar energy. Additionally, for solar energy investments, it is highly essential to predict the annual average solar radiation on the region. The literature indicates that the Ångström formula has, most of the time, been used for such estimations. However, in this paper, for the first time in literature, monthly average daily global radiation on the horizontal surface of Karaman region was calculated by means of spline interpolation, cubic spline regression, local polynomial regression, and Ångström methods, and the outcomes were compared. As a result, it has come out that the cubic spline method gives the best-fit values. Accordingly, it is concluded that the cubic spline model offers, statistically, better estimation results.