As of December 2023, 15 states offered a child tax credit (CTC) on their state individual income tax, but the structure and size of these credits varied significantly. This report summarizes and explains the policy levers involved in designing a state CTC, and it uses the Tax Policy Center state tax model to analyze multiple versions of a hypothetical CTC in four states that currently do not offer one: Illinois, Michigan, Nebraska, and Virginia. In each state, we adjusted the amount of the credit, applied different child age eligibility restrictions, limited and expanded the income eligibility requirements, and modeled both refundable and nonrefundable versions of the credit to show how different policy decisions affect both the credit’s annual revenue cost and the distribution of its benefits.