After doing some research, I've found that the best month to buy a car in the United States is typically December. This is because dealerships are eager to meet their annual sales goals and clear out inventory for the new year, offering attractive incentives and discounts. Additionally, the holiday season often means less foot traffic in showrooms, giving buyers more negotiating power. However, keep in mind that selection may be limited as the month progresses. Ultimately, it's essential to do your research and be prepared to negotiate for the best deal, no matter when you choose to buy.