Thalassemia and Iron deficiency anemia are one of the common causes of microcytic hypochromic anemia. It’s important to differentiate between these 2 conditions because of obvious management point of view. Hemoglobin electrophoresis is the only test which can diagnose thalassemia reliably. But it is costly and not available widely particularly in developing countries including India. For this reason it is important to have some tool which can differentiate between thalassemia and iron deficiency anemia during routine OPD practice. Mentzer index calculator can give a fair idea of diagnosis on the basis of a simple complete blood count report. The only 2 input parameters include Mean corpuscular volume (MCV) and Red Blood cell count (RBC count) which is available in CBC report.This App will give you a fair idea about the presumptive diagnosis. Of course as a primary care physician you must take into account the clinical features and other lab parameters.