As the demand for total hip arthroplasty (THA) and total knee arthroplasty (TKA) increases, so does the financial burden of these services. Despite efforts to optimize spending and bundled care payments, THA and TKA costs still need to be assessed. Our study explores the relationship between perioperative costs and length of stay (LOS) for THA and TKA. A total of 614 patients undergoing THA or TKA at a single private practice with LOS from zero to 3 days were identified. All patients were insured by private or Medicare Advantage insurance from a single provider. Primary outcomes included total costs and their relationship with LOS, classified into surgeon reimbursement, facility costs, and anesthesia costs. Secondary outcomes included readmission rates and discharge disposition. Analyses involved Student t-test, analysis of variance, and chi-square tests. Longer LOS was associated with increased total, facility, and anesthesia costs. Costs for THA patients were stable except for reduced surgeon reimbursement with longer LOS. Patients undergoing TKA experienced an increase in facility costs with longer LOS. Total facility and anesthesia costs increased with LOS for Medicare Advantage patients, but surgeon reimbursement remained stable. Privately insured patients experienced higher total and facility costs but stable surgeon reimbursement and anesthesia costs regardless of LOS. Our study shows an increase in total cost with longer LOS, especially pronounced in privately insured patients. A notable reduction was observed in the surgeon reimbursement for Medicare Advantage patients with extended LOS. These findings underscore the need for efficient surgical practices and postoperative care strategies to optimize hospital stays and control costs.