If it is a "retail" key, you can reuse it indefinitely........as long as it is on 1 PC at a time.
Results vary if it is NOT a retail key. Microsoft seems to be less strict than it used to be about the distinctions between keys.
If your current installation came as part of a "pre-built" PC, it's not likely to be retail.
If you bought the license by itself when building your own PC, it could be any type of license.