The patients in NICU (Neonatal Intensive Care Unit) are more likely to get portable X-ray often while they are in the hospital. These patients potentially may get relatively more exposure dose in total in a short period of time. We developed a software to analyze the exposure dose for the patients in the incubator, which is called PIETAII (Patient Information of Exposure dose Total Analysis in NICU). Then, we compared the accuracy of PIETAII and SDEC (surface dose evaluation code) based on customary method. Using the 5 cm body thickness with exposure setting of 50 kV, 1 mAs, relative error between the customary method and the calculated dose by PIETAII and SDEC were 1.96% and 32.35%, respectively. PIETAII is a useful software to estimate the entrance surface dose using the exposure setting.