This depends on a few factors like how hot your oven temperature is and the thickness and size of the chicken, but generally at 400 degrees F it takes 25-30 minutes to bake chicken breasts. A lower temperature like 375 degrees F will take slightly longer running the risk of drying out the chicken, while a higher temperature like 425 degrees F will take longer and you risk overcooking the outside while the middle still isn't quite done.