You have to budget your income and expenses to determine the amount you can afford to spend on a car. Make a list of your estimated income, and then list all of your expenses. Don’t forget to include every last thing you need to live comfortably. When you have that list completely, you will see the amount that you will be able to spend on a car payment. It is best to plan the purchase of a car ahead of time so you can have a sizeable down payment available when you are ready to sign the papers.