How long does a provisional application for patent last?

A provisional application for patent lasts 12 months from the filing date. The U.S. Patent Office will not grant extensions for any reason. The inventor(s) must file a non-provisional patent application (NPA) within that period to take advantage of the provisional application's filing date. If not, the provisional application is declared abandoned. Another provisional application or even a full patent can still be filed, just without the benefit of the earlier filing date.