The article is devoted to the analysis of the specifics of budget planning when using CDK4/6 inhibitors (ribociclib, palbociclib, and abemaciclib) for the treatment of HER2-negative metastatic breast cancer in postmenopausal patients. Based on clinical trial data and cost analysis, ribociclib was found to be advantageous in terms of efficacy and cost-effectiveness. According to randomized clinical trial data, not all the CDK4/6 inhibitors demonstrated a statistically significant increase in overall survival in combination with aromatase inhibitors. Ribociclib in combination with aromatase inhibitors has a statistically significant difference in overall survival compared to aromatase inhibitor monotherapy and reduces the risk of death by 24%. More than 30% of patients receiving CDK 4/6 inhibitors therapy require dose reduction, which is accomplished in a variety of ways depending on the dosage forms. Dose reduction has an impact on the cost per CDK4/6 inhibitors treatment cycle: before dose reduction, the cost per cycle of therapy with palbociclib and abemaciclib is lower compared to ribociclib. At the first dose reduction, the cost per cycle of therapy for all CDK 4/6 inhibitors is comparable. At the second dose reduction, the cost of a cycle of therapy on ribociclib is half that of palbociclib and abemaciclib. When planning the budget for providing CDK4/6 inhibitors to patients with metastatic cancer, it is necessary to consider a number of key characteristics of drugs that affect the costs and organization of the treatment process. An important aspect of budget planning is forecasting the need for drugs, considering the need for dose reduction. For ribociclib, the calculation of annual need is simplified by the possibility of reducing the number of tablets taken, which allows the use of a single dosage form, whereas for palbociclib and abemaciclib it is necessary to purchase several dosage forms with different dosages, which complicates planning, reduces the predictability of consumption, and requires additional administrative measures.