The aging brain causes the problems associated with decision making, memory loss, language problems, personality problems, and changes in behavior. Physicians decide treatment based on disease progression and the patient’s overall health. Alzheimer’s disease (AD) and Mild Cognitive Impairment (MCI) are two majorly reported clinical abnormalities in today’s time. The adversity of the disease can be controlled with timely diagnosis and choice of treatment modality. Noninvasive treatment like transcranial electrical stimulation has shown effective results in drug-resistant and early diagnosed patients. Transcranial Direct Current Stimulation (tDCS) uses low electrical direct current through specialized stimulating electrodes. The induced electric field within the targeted area can be measured in vivo with greater accuracy with its limitation of applicability to humans. Characteristics of the tissue changes with its compositional variation with different tissue mass like Cerebrospinal Fluid (CSF), Skull, Skin, Gray matter, and White matter. Computational modeling of tissue characteristics and external stimulation provides a better solution for the effective measurement of spatial electric field distribution. The effectiveness of treatment greatly depends on targeted electrical stimulation with precise localization of stimulation electrodes. Apart from the location of the stimulation electrodes, electrode size, shape, duration of stimulation, the patient’s specific anatomy, the strength of the current, and conductivity of tissue alter the treatment efficacy and clinical outcome. In this study, we have obtained Magnetic Resonance Imaging (MRI) images from the AD neuroimaging initiative to create patient-specific head models for AD and MCI patients. Simulation of Non-invasive Brain Stimulation (SimNIBS) open-source software used for calculating electric field induced by transcranial electrical stimulation. Obtained results were compared for both patient groups to know the variation of electric field distribution across the head regions. Results suggest that electric field distribution varies with selected stimulation parameters and patient-specific head models. Increasing current intensity by 25% of 1 mA results in a 25% increase in electric field strength, whereas a 50% increase in 1 mA of current intensity results in a nearly 49.46 % increase in electric field strength of Left Dorsolateral Prefrontal Cortex (LDLPFC). With standard conductivities of head tissues and uniform stimulation parameters for both the patients, we obtained varied electric field strength which signifies the tissue abnormality caused by neurodegenerative disease.