Objective: To determine Beyond Use Date (BUD) of cetirizine hydrochloride syrup preparation by analyzing cetirizine concentrations using High-Performance Liquid Chromatography (HPLC) with an Ultraviolet (UV) detector. Methods: The analysis was carried out using mobile phase acetonitrile-phosphate buffer pH 3 (50:50 v/v), flow rate 1 ml/min with isocratic elution, and detected using a UV detector at 232 nm. The BUD was determined by measuring the cetirizine level in the syrup sample since the primary packaging was opened (day 0) for 5 w of storage. Results: The analytical method was selective and specific. The linearity results show a correlation coefficient (r) of 0.9998 in the 4-32 g/ml concentration range. The limit of detection (LOD) and limit of quantification (LOQ) values were 0.5 µg/ml and 1.7 µg/ml, respectively. The method satisfies accuracy, precision, robustness, and ruggedness criteria. The data showed a decrease in cetirizine concentration level in preparation within 5 w. Conclusion: This study successfully determined the BUD of cetirizine hydrochloride syrup by analyzing cetirizine concentrations using HPLC with a UV detector. The results revealed a progressive decrease in cetirizine concentration over five weeks of storage, and the BUD was established at 25 d. This finding is significant, providing valuable guidance for pharmacists and healthcare providers in managing the use of the medicine after the primary packaging is opened. © 2025 The Authors.