When should I file my patent application?

On Valentine’s Day morning in 1876, Alexander Graham Bell filed an application for the telephone – which was to become one of the most valuable patents ever issued. By incredible coincidence, Elisha Gray arrived at the Patent Office later that same day with his independently developed telephone invention. After years of litigation, Bell received the patent, launching the modern telecommunications industry. Gray slipped into relative obscurity.

 https://en.wikipedia.org/wiki/Elisha_Gray

https://en.wikipedia.org/wiki/Elisha_Gray

Although prior to March 16, 2013, the United States granted patents to the earliest inventor, the current law follows the first-to-file system used by most of the rest of the world, and grants patents to the first inventor to file a patent application.

The best advice for any entrepreneur is to file early and to file often. Filing patent applications on developing ideas does not need to be expensive. A provisional patent application can be self-prepared and filed with the Patent Office for around a hundred dollars. Provisional applications can be thought of as placeholder applications, and while they are never examined by the Patent Office, they provide a filing priority date for invention details which are provisionally disclosed.