Swelling soils cause serious damage to engineering structures, and they pose a problem worldwide. The fluctuation of water content is known as one of the most important factors that cause the swelling pressure of soils, especially for soils found in arid and semi-arid regions. The swelling soils found in these regions are exposed to cycles of volume increase and decrease in the rainy and dry periods. Thus, low-rise buildings and infrastructure constructed on/in these soils are exposed to potential damage. Although the relationship between swelling parameters and the physical-index properties of soils have been investigated in detail in previous research, the effect of variations in the initial water content on the swelling pressure of soils has not yet been sufficiently studied. For this reason, samples were prepared at the same dry unit weight and with different initial water contents to examine the effect of water content on the swelling behaviour of soils. According to swelling test results reported here, there is a statistically significant linear relationship between initial water content and swelling pressure. Some predictive empirical models with high correlation coefficients are obtained. In addition, a new approach called “Swelling Pressure Designation (SPD)” is recommended to be used for predicting the swelling pressure of soils of any water content.