The cooking time for a chicken breast at 400°F (205°C) can vary depending on the size and thickness of the chicken breast. A general guideline is to cook a 4-ounce (113-gram) chicken breast for 20-25 minutes, a 6-ounce (170-gram) chicken breast for 25-30 minutes, and an 8-ounce (227-gram) chicken breast for 30-35 minutes.
However, it’s important to note that the only way to ensure that the chicken is fully cooked and safe to eat is to use a meat thermometer to check that the internal temperature of the chicken reaches 165°F (74°C). Insert the thermometer into the thickest part of the chicken breast without touching the bone and wait for a few seconds until the temperature stabilizes. If the temperature is below 165°F, continue cooking the chicken and check the temperature again after a few minutes.