Purpose: Research and lived experience demonstrate that sexual orientation and gender identity (SOGI) can change over the life course; however, little empirical work exists to understand the prevalence of such changes. To address this gap, we used data from a large nationally representative panel of adults and adolescents to assess changes in self-reported SOGI over time and identify trends by sex assigned at birth, age, race and ethnicity, and survey mode. Methods: We reviewed SOGI data collected between 2014 and 2022 for a sample of 19,469 adults and 970 adolescents. Up to eight SOGI measurements per panelist were available over the nine-year period, collected through a combination of panel recruitment and demographic refresh surveys and topic-specific surveys. Results: Among adults older than 18 years, 4.1% reported a change in sexual orientation and 3.6% reported a change in gender identity. Among teens, who are developmentally more apt to change identity, 13.5% reported a change in sexual orientation and 9.3% reported a change in gender identity. Conclusions: Findings demonstrate that SOGI can change over time, particularly for adolescents, so it is important to re-ask SOGI questions to ensure current information. We recommend re-asking SOGI questions at least every three years of adults and every two years of adolescents. Potential undercounting of sexual and gender minority (SGM) respondents decreases visibility and our ability to understand health and economic disparities affecting these populations. Improvements in SOGI measurement can help advance data quality and, ultimately, evidence-based interventions in support of SGM communities that these data help to inform.