ImportanceThe 2021 expanded Child Tax Credit provided advance monthly payments to many US families with children from July through December 2021 and was associated with a reduction in food insufficiency. Less is known about the effect of the discontinuation of monthly payments.ObjectiveTo assess whether the discontinuation of monthly Child Tax Credit payments was associated with subsequent changes in food insufficiency among lower-income US households with children.Design, Setting, and ParticipantsThis population-based cross-sectional study used data from the Household Pulse Survey, a recurring online survey of US households conducted by the US Census Bureau, from January 2021 to March 2022. This study estimated difference-in-differences regression models for households making less than $50 000, less than $35 000, and less than $25 000 annually, adjusting for demographic characteristics and state of residence. The estimation sample of households making less than $50 000/y included 114 705 responses, representing a weighted population size of 27 342 296 households.ExposuresReceipt of monthly Child Tax Credit payments, as measured by living in a household with children during the period of monthly payments from July through December 2021.Main Outcomes and MeasuresHousehold food insufficiency, as measured by a respondent indicating that there was sometimes or often not enough food to eat in the household in the previous 7 days.ResultsAmong 114 705 households making less than $50 000/y, respondents were predominantly female (57%); White (71%); not of Hispanic, Latino, or Spanish origin (79%); had high school or equivalent education (38%); and were unmarried (70%). Following the discontinuation of monthly Child Tax Credit payments, food insufficiency in US households with children increased by 3.5 percentage points (95% CI, 1.4-5.7 percentage points) among households making less than $50 000/y, 4.9 percentage points (95% CI, 2.6-7.3 percentage points) among households making less than $35 000/y, and 6.2 percentage points (95% CI, 3.3-9.3 percentage points) among households making less than $25 000/y. These estimates represent a relative increase in food insufficiency of approximately 16.7% among households making less than $50 000/y, 20.8% among households making less than $35 000/y, and 23.2% among households making less than $25 000/y.Conclusions and RelevanceIn this population-based cross-sectional study, discontinuation of monthly Child Tax Credit payments in December 2021 was associated with a statistically significant increase in household food insufficiency among lower-income households, with the greatest increase occurring in the lowest-income households.