Long-term forecasting of key macroeconomic indicators such as population is very important for future development policy-making. Population plays an important role in economic decision-making, social security and economic growth. So it is important to develop a good model for predicting economic indicators. In order to improve the growth model, we introduce a new model called Exlog Weighted Sum Model for predicting macroeconomic indicators. This model combines both exponential and logistic models. The proposed model was tested for predicting Mongolian population up to 2040.