Drug cost is considered an important factor in treatment compliance for cancer patients. However, it is difficult to calculate individual drug costs. We were previously unable to provide sufficient information on costs to cancer patients starting drug therapy. Therefore, we developed a tool, in the form of a spreadsheet, which calculates drug costs for breast cancer treatment. This software tool runs on every terminal for electronic medical charts in our hospital. To evaluate the tool, we created 10 fictional breast cancer patient sets. Five pharmacists calculated the drug costs for a single regimen using method A (without software) and method B (with software). The pharmacists then calculated the drug costs for 3 regimens in the same way. We compared the time taken to calculate costs using method A and method B. For the single regimen, the mean time for method B (22.6±6.9 s) was 6.4-times shorter than that for method A (145.2±28.3 s, p<0.0001). For the 3 regimens, the mean time for method B (35.5±5.0 s) was 8.9-times shorter than that for method A (315.8±43.1 s, p<0.0001). The differences observed were statistically significant. By using the software, we were able to shorten the calculation time for drug costs, and therefore, alleviate the burden on medical staff.