By filing a provisional patent application, you set a 12-month clock called the pendency period. During the pendency period, the United States Patent and Trademark Office does not examine the application on its merits. Before this period is over, you must either file a regular patent application claiming the priority of the provisional one or convert the provisional application into a regular one. Only then will the USPTO examine the application. If you do not follow up, you may lose the right to file for a patent on the invention.
The initial cost of filing a provisional patent application is slightly less than the cost of filing a regular application. While this may appeal to cash-strapped inventors, the savings is illusory. In addition to paying fees for filing the provisional application, inventors must also pay regular filing fees when they file the regular application or convert the provisional application. This could end up costing you a few hundred dollars, depending on the type of patent you are seeking.
An inventor cannot sell, publish or publicly use his invention in the U.S. more than one year before he files a patent application for the invention. Inventors who engage in such acts during the pendency period risk their right to patent the invention if they inadvertently let the provisional application lapse without converting it or filing a regular application.
Provisional patent applications typically contain limited information because the inventor is pressed for time or is uncertain about the scope of the disclosure. Disclosing partial information is not the best practice because only the disclosed information will receive the early filing date. If you must file provisionally, the best practice is to disclose as much as possible about how to make and use the invention. By making as full a disclosure as possible, your invention will be protected if you have to convert it into a regular application at the last minute.