This is all up to the airline that you chose. Some airlines allow you to check one bag up to 50 pounds for free, and then charge an additional fee for each bag after that. Some airlines offer a small fee for the first check bag and a higher price tag for each subsequent bag. As a general rule of thumb, you should ensure that your back does not exceed 50 pounds before heading to the airport. If your bag weighs more than 50 pounds, you may have to pay the heavy cost of paying for two checked bags instead of one.