I’m not an expert. I’m just a guy who likes to think about stuff.
You’ve written a provisional application. You now have 12 months to file a utility application. What if you have new ideas to add to that invention?
You have options. If you come up with those new ideas within 12 months of filing a provisional application, you can file multiple provisional applications. This option is a helpful one since the provisional filing fee is only $130 for small entities. When you eventually file the utility application, you can claim priority to all the provisional applications. The patent examiner will look over the provisional applications to ensure that they fully disclose the invention claimed in the utility application.
The second option is to file a continuation in part application. Picture this. You’ve filed a utility application. After filing the utility application, you’ve thought of new ideas to add to the invention. You can file a continuation in part application, while the original utility application is pending, to include those new ideas to the invention. The filing date for the continuation in part application will not be the filing date of the original utility application, though. The filing date for a continuation in part application is the filing date of that application. So for instance, if you file a utility application on June 1, 2016, and you file a continuation in part application on July 15, 2017, the filing date of the continuation in part application will be July 15, 2017. The cost of filing a continuation in part application is the same as for the original utility application ($730 for small entities). Make sure that you file a continuation in part application before the original utility application issues as a patent, though. Failure to do so will result in the original utility application potentially being used prior art against you, and the continuation in part application may get rejected.
As you can see, generating new ideas before the utility application is filed is a cheaper option. During those 12 months, try as best as you can to do further experimentation to come up with new ideas for your invention. But if you have new ideas after filing the utility application, you always have the option of filing a continuation in part application.