Modified kraft pulping has shown to improve the quality of pulp by achieving lower K numbers and/or increasing the pulp strength, but its implementation is based on empirical knowledge and is installation-specific. One of the recommendations to implement modified cooking is that of leveling out the effective alkali concentration throughout the cook, which demonstrates the subjectivity of the approach. To apply a universal methodology that defines the specific effective alkali level or profile to achieve a desired pulp, a reliable effective alkali dynamics (model) is required. Effective alkali is consumed during the bulk phase mainly for delignification, but its concentration is also affected by supplying white liquor at different times or points. If a model describes the effective alkali dynamics properly based on delignification and process characteristics, then a more general methodology could be developed to define the required effective alkali levels. A model that is easy to use, has real-time features for optimization and process control purposes, and is based on bulk liquor measurements is presented. In this work, a series of modified kraft experiments were performed where the effective alkali and dissolved lignin are measured in situ. Once the lignin and effective alkali measurements are collected, a modification of the classical fundamental-type model is performed to represent the experimental data. It is shown that the typical thought of having the effective alkali dynamics proportional to delignification seems unsuitable for modified kraft pulping, where alkali profiling is used.