This study focuses on the evaluation of in-situ permanent deformation in fine-grained soils through the application of a specially designed repeated Light Weight Deflectometer (LWD) test. The primary objective is to investigate how water content and applied stress levels influence permanent deformation in the field. In addition, the study aims to assess the usefulness of LWD derived data in predicting permanent strain. The results indicate a significant correlation between permanent deformations and key parameters such as number of load cycles, applied stress levels and water content. It is observed that permanent deformations increase proportionally with these variables, particularly at higher water contents and stress levels. The soil exhibits an increased susceptibility to accumulating permanent deformations that persist even after numerous LWD loadings. In response to these findings, a predictive model is presented to estimate accumulated permanent strain, which shows a commendable fit to the data for moisture contents up to 22%, corresponding to an average water content of 19%. Ultimately, this research highlights the important role of water content and applied stress levels in determining the permanent deformation characteristics of fine-grained subgrade soils. The study also provides a valuable predictive model derived from repeated in-situ LWD measurements, providing critical insights into the field permanent deformation behaviour of subgrade soils. This simple and time-saving test improves engineering practice for pavement design and construction.