Singh JA, et al. - Future projection of total hip and knee joint arthroplasty (THA, TKA) use in the United States to 2040 were developed in this work using the 2000–2014 US National Inpatient Sample (NIS) combined with Census Bureau data. Polynomial regression was used to account for the nonlinearity and interactions between the variables, assuming the underlying distribution of the number of THA/TKA to be Poisson distributed. In the United States, for THA, predicted total annual counts for 2020, 2025, 2030, and 2040 are (in thousands): 498 (475, 523), 652 (610, 696), 850 (781, 925), and 1,429 (1265, 1615), respectively. Predicted total annual counts for primary TKA for 2020, 2025, 2030, and 2040 are (in thousands): 1,065 (937, 1,211), 1,272 (1,200, 1,710), 1,921 (1,530, 2,410), and 3,416 (2,459, 4,745), respectively. Findings suggest that in the future, the use of THA and TKA are expected to show significant increases in the United States if the current trend continues. For both females and males, in all age groups, primary THA and TKA use is projected to increase.