The amount of time it takes to cook chicken breast in the oven will depend on the size and thickness of the chicken breast, as well as the desired level of doneness. As a general rule, a boneless, skinless chicken breast will take about 20-30 minutes to cook at 400 degrees Fahrenheit. However, it is always best to use a meat thermometer to check for doneness, as the internal temperature of the chicken should reach at least 165 degrees Fahrenheit to ensure that it is cooked through.