Background: During the COVID-19 pandemic, the annual US inflation rate increased from 1.2% in July 2020 to 8% in July 2022. It has since declined to 3.4% (December 2023). This study examined the prevalence of stress due to inflation during a period when it declined from 8.2% in September 2022 to 3% in June 2023 and its association with demographic and social determinants of health (SDOH). Methods: We conducted a cross-sectional analysis of the online Household Pulse Survey (HPS), which surveils the experiences of US households. Beginning September 2022, HPS initiated data collection on “stress due to inflation” through a question on how stressful the increase in prices in the last 2 months has been. Participants could respond: very, moderately, a little, or not stressful. We analyzed data on working-age adults (18–64 years) who responded to the above question of stress due to inflation during 14–26 September 2022 (N = 32,579) and 7–19 June 2023 (N = 36,229). We used replicate weights in chi-squared tests and ordinal logistic regression analyses controlling for gender, age, race and ethnicity, COVID-19, COVID-19 vaccination, health insurance, and SDOH, including education, lost employment income, poverty status, marital status, food affordability, and region. Results: The prevalence of stress due to inflation (price increases being very or moderately stressful) significantly increased from 76.9% in September 2022 to 78.9% in June 2023. The odds of stress due to inflation were higher for individuals with the following characteristics: female, transgender, having income below 400% of the federal poverty line, having lost employment income, not being able to afford food, had long or acute COVID-19, and did not have a COVID-19 vaccine. Conclusions: More than three quarters of working-age adults in the US experienced stress due to inflation. Despite a declining national inflation rate in recent months, stress due to inflation has significantly increased among working-age adults. Inflation-related stress warrants further research and policy attention.