To be eligible for the premium tax credit, your household income must be at least 100 – but no more than 400 – percent of the federal poverty line for your family size, although there are two exceptions for individuals with household income below 100 percent of the applicable federal poverty line. The poverty line for a family of 6 in 2018 was $33,740.  

Remember that simply meeting the income requirements does not mean you’re eligible for the premium tax credit. You must also meet the other eligibility criteria. 

For more detailed information about this tax credit, see here: https://www.irs.gov/affordable-care-act/individuals-and-families/eligibility-for-the-premium-tax-cre...