Line 11 on Form 1040 is your adjusted gross income. Line 2a on Form 8962 is your modified adjusted gross income. These two numbers may not be the same, as in your case.

For the premium tax credit, the modified adjusted gross income is calculated by adding back nontaxable income such as tax exempt interest, foreign earned income, and nontaxable social security benefits to your adjusted gross income. Since you received the lump sum social security benefits in 2024, this income is added to the household income.