A patent application should define an invention that is novel (new) and non-obvious over what is already known to the public. A patent application will be judged against what was known to the public before the filing date of the patent application. This means it is important for a patent application to be filed as soon as possible to establish an early filing date.
If patent applications are required in more than one country, there would be a proportionate increase in costs as multiple patent applications would then have to be filed around the world. This is far from ideal at such an early stage of an invention’s life. Fortunately, the patent system provides a mechanism to allow further patent applications to be filed up to a year after an earlier patent application filing without sacrificing an early filing date. This mechanism is called priority.
The further patent applications receive both a filing date (the date they were filed) and also a priority date (the filing date of the earlier patent application). Crucially, the further patent applications are judged against what was known to the public before their priority date, and not their filing date. Hence, for the purposes of assessing novelty and non-obviousness, the further patent applications are treated as if they were filed on the same day as the earlier patent application
Furthermore, the maximum life of a patent is not shortened by claiming priority when a patent application is filed. This is because the maximum life of a patent is calculated as 20 years from the filing date, and not the priority date.
How do I claim priority to an earlier application?
There are some requirements for a further patent application to claim priority from an earlier patent application:
the earlier patent application must have been filed in a recognised country/state (most countries are recognised);
the applicant of the further patent application must be the same applicant (or successor in title) as for the earlier patent application;
the further application must be filed within one year of the earlier application;
the further patent application must include at least some of the same subject matter as the earlier patent application (but can add new subject matter); and
the earlier patent application must be the first patent application to disclose the invention (i.e. you cannot defer beyond one year from your first patent application by waiting a year to file a second patent application that claims priority from the first patent application, and then waiting another year to file a third patent application that claims priority from the second patent application).
Can subject matter be added in a further patent application?
Yes, a further patent application can include new subject matter. For example, if an improvement is developed to an invention in the year after first filing a patent application, a further patent application may be filed describing the original invention and the improvement. This further patent application may claim priority from the earlier patent application. However, the priority date can be claimed only for the subject matter of the original invention, and the new subject matter will receive the filing date of the further patent application.
Can I claim multiple priorities?
Yes, it is possible to claim priority to two or more earlier patent applications.