Short answer: As soon as you decide you are serious about trying to protect a new idea. Seriously.
If you really don’t know much or anything about patents and patenting inventions, there are a few very basic things that would be good to know right away before you do much more than think about an idea. If you are serious and genuine in your interest, most patent attorneys will spend at least 10 -15 minutes without any charge in an initial call to give you a basic orientation on what you need to know and direct you to resources to help you learn more on your own.
The biggest reason to talk to a patent attorney as soon as possible is to try to avoid the one thing that seems to most often trip up individual and new inventors – a non-confidential disclosure of the invention more than a year before filing a patent application. Such a non-confidential disclosure usually eliminates the opportunity to obtain patent protection for an invention. Whenever I get a call from a new inventor, the first question I ask (after telling him or her not to divulge any confidential information because I am not yet engaged) is, “how long ago did you tell anyone about the invention in a manner that was not confidential?” I can’t tell you how many times the answer I have gotten back is some time more than a year earlier, sometimes many years earlier. When that happens, there is not much I can do to help.
If you talk to a patent attorney before you make that initial, non-confidential disclosure, you can get a sense of your best options on how to proceed while minimizing the possibility of losing rights in your invention. Depending on the circumstances and your budget, options include just keeping things secret, entering into confidentiality agreements before making a disclosure and/or filing at least a very basic provisional application.
So don’t hesitate to make that initial call. It likely won’t cost you anything, but it could save you a whole lot later.