With the advancement of targeted therapies such as radionuclide therapy, alpha emitting radionuclides, including actinium 225, have gained considerable importance in the treatment of therapy resistant tumors due to their high linear energy transfer (LET) and short particle range. In this study, the time dependent activity behavior of the actinium 225 decay chain was investigated through numerical modeling of the decay chain differential equations using MATLAB, along with experimental measurements performed by gamma ray spectrometry employing an HPGe detector. Quantitative results demonstrated that the relative difference between theoretically calculated activities and experimentally derived values obtained from gamma emitting daughter nuclides (francium 221 and bismuth 213) remained below 2%, and that applying uncertainty weighted averaging led to a significant improvement in the agreement between theoretical and experimental data. Furthermore, temporal analysis indicated that equilibrium for francium 221 and bismuth 213 was established within less than 1 hour and 20 hours, respectively. Long term monitoring of the sample over a six month period confirmed the absence of any measurable radionuclide impurities. These findings demonstrate that numerical modeling of the decay chain provides a reliable tool for the quantitative estimation of actinium 225 activity and for improving dosimetric calculations in targeted alpha therapy.