A filing fee must be sent in for every patent application that is filed. However, the filing fee is not due immediately; the applicant may choose to send it in later during the prosecution.

There are different fees for different application types and different fees for the various documents and petitions that may need to be sent in during the prosecution. The fees constantly change so it's recommended that individuals always check on the current fee before sending any money in.

As you can imagine, filing a patent application is a fairly expensive ordeal. To make matters worse, there are more fees involved than just a filing fee; the PTO charges a fee for virtually every step.

At best, a patent applicant should expect to pay a filing fee and an issue fee. In addition, maintenance fees must be paid on utility patents that issue. These are paid after the patent issues to keep it from expiring.

At worst, an applicant may have to pay these fees plus fees for several petitions, fees for late filed forms, extensions of time, disclaimers, appeal-related fees and fees for a request for continuing examination among many other fee related extras. We will discuss all these 'extras' later, but for now just realize that filing a patent application is expensive and requires sending in numerous fees. The PTO does not refund money if the patent application is ultimately rejected.