Objectives. To estimate gains in the prevalence of individuals who had ever been tested for HIV overall and by subpopulations from increases in the percentage of persons who had a routine checkup and were tested. Methods. We used data from the 2019 Behavioral Risk Factor Surveillance System to determine the prevalence of individuals who were ever tested for HIV and the prevalence of missed opportunities for HIV testing among those never tested in the United States. We assessed the effect of absolute percentage increases in having ever been tested among those who had a past-year routine checkup on increasing the overall prevalence of having ever been tested. Results. In 2019, 49.5% of US adults had ever been tested for HIV; 34.5% had a missed opportunity. A 50% increase in testing at routine checkups would increase the prevalence of having ever been tested to 84.0%. Increases in the prevalence of having ever been tested (≥ 85%) was highest among persons aged 35 to 54 years, Black persons, persons who were female at birth, persons with health insurance, and persons reporting HIV risk behaviors. Conclusions. Fully incorporating HIV screening into primary care would greatly increase the proportion of US adults who have been tested for HIV. Public Health Implications. Continued efforts to promote HIV testing, including implementing routine screening in clinical settings, will help ensure that all US adults know their HIV status.