Why improvements need their own date
Each claim in a patent application is entitled to the date of the first document that properly disclosed it. Your original provisional secures a date for the invention as it was described on the day it was filed. An improvement developed afterwards isn't in that document, so it can't take that date, however closely it is related.
The improvement needs its own date, and that date is the one against which its novelty and inventive step will be judged. Anything made public before it, including your own product launch, a competitor's filing or an article in a trade journal, can be cited against claims to the improvement.
Option one: a further provisional application
The first option is to file a further provisional application describing the improvement as soon as it is developed. It is sometimes called a co-pending provisional, because it runs alongside the first one.
The improvement gets an immediate filing date. When the complete application is filed, it claims priority from both provisionals. Claims to the original invention rely on the first provisional's date, and claims to the improvement rely on the second. A PCT application can claim priority from several earlier applications in the same way, so this works internationally too.
There are two practical points to keep in mind. The 12-month deadline for filing the complete application still runs from the first provisional, so a further provisional doesn't extend the timeline. And the further provisional needs the same care as the original. It must describe the improvement clearly and completely enough for a skilled person to put it into practice, or its date will be no more reliable than a thin first provisional's would be. We explain why in the pitfalls of a poorly prepared provisional patent application.
Option two: include it in the complete application
The second option is to wait and include the improvement when the complete application is prepared at the end of the provisional period. The improvement is described in the complete specification and claimed alongside the original invention, usually in dependent claims or a further independent claim.
This saves the cost of a separate filing, and for many improvements it is entirely sensible. The trade-off is the date. The improvement takes the filing date of the complete application, which may be many months after the improvement was actually developed. Everything published in the meantime counts against claims to it.
Choosing between them
The question is how much risk sits in the gap between developing the improvement and filing the complete application.
A further provisional is usually the better choice if you are about to disclose the improvement, by launching a product that incorporates it, showing it to investors or customers, or publishing about it. Once disclosed, the improvement becomes prior art against itself in countries without a general grace period, such as Europe and China. Our article on patent grace periods country by country explains where you are exposed. The same applies if the improvement is commercially important, if competitors are active in the same space, or if the complete application is still many months away.
Deferring to the complete application is usually reasonable if the improvement will stay confidential until then, if it is a refinement rather than a commercially significant step, or if the complete application is due within a few weeks anyway, so the gap is small.
The question is not whether an improvement can be protected, but from what date. That date decides what can be used against it.
What you can't do after the complete application is filed
The provisional period is the window for adding new technical material. Once the complete application is filed, section 102 of the Patents Act 1990 prevents amendments that would add matter not disclosed in the specification as filed. Improvements made after that point need a new application with its own date.
That new application has a further hazard. Your own complete application is published about 18 months after its priority date, and once it is published it becomes prior art against any later application, including your own. An improvement that is an obvious step from what you have already published may then not be patentable. If you expect further development, it pays to capture improvements while the provisional period is still open, or at least before your earlier application is published.
A practical approach
We encourage clients to tell us about improvements as they happen rather than saving them up for the complete application. For each one we look at its commercial importance, when it is likely to be disclosed and how far off the complete application is, and then recommend either a further provisional now or inclusion in the complete application later. This is one of the main benefits of starting with a provisional, as we explain in our approach to patent applications.
If you have improved your invention since filing, contact Patentec for a free initial consultation. We'll help you decide whether the improvement needs its own filing date now or can wait for the complete application.