The average length of treatment time for metal braces usually ends up being around 2 years, whereas the average length of treatment time for Invisalign ends up being around 18 months. That being said, the exact length of orthodontic treatment time will be different on a patient-by-patient basis. There a variety of reasons why it is hard to gauge an exact treatment time for any given orthodontic case.
The length of treatment time will largely depend on the severity of the case. A patient with very minor spacing issues may only require six months of orthodontic treatment, while a patient with severe malocclusion may take longer than two years. Only your orthodontist will be able to give you a better idea of how long treatment will likely be in your particular case.
Other issues can also come into play. If a patient received early intervention treatment, then their subsequent treatment may be shorter. If a patient is not diligent about taking care of their braces or aligners, or if a patient misses several of their appointments with the orthodontist, it could cause a delay in treatment. The same holds true if a patient experiences oral health issues during treatment, such as gum disease.