Nuances of divisional patent practice in Australia and New Zealand

A recent opposition decision by the New Zealand Patent Office in Resmed Pty Ltd v Fisher & Paykel Healthcare Limited [2026] NZIPOPAT 6 provides a useful reminder of how divisional patent practice in New Zealand differs from that in Australia, and the traps unsuspecting applicants can fall into in both jurisdictions.

While not the substance of the Resmed decision, the Assistant Commissioner considered whether a divisional application should be "post-dated" (i.e., treated as having been filed on the date it was submitted at the Patent Office). No decision was ultimately issued in this respect, as the Assistant Commissioner found the application to be invalid for other reasons, but the question of "post-dating" brings to mind how divisional patent practices diverge between Australia and New Zealand.

Divisional filing date

In Australia, a divisional application is entitled to divisional status under s 79B of the Patents Act 1990 (Cth) if it is "for an invention disclosed in the specification filed in relation to the first application". Essentially, provided the divisional specification as filed contains an invention disclosed in the parent application, new matter can be filed and claimed in the divisional application and the patent date still be the same as that of the parent application (although adding matter may have implications for the priority date and best method, as discussed below).

By contrast, a divisional application is entitled to divisional status under s 34 of the Patents Act 2013 (NZ) if it is "for any part of the subject matter of the parent application". Essentially, provided no new matter is added to a divisional specification relative to its parent, it will be "ante-dated" so as to be treated as having been filed on the same day as the parent application. Conversely, the addition of any matter that is not supported by the parent application will result in the divisional application being post-dated.

Australia also allows for applications to be converted to divisionals of other applications under certain conditions – a mechanism that has proven useful in some circumstances when faced with self-published "whole of contents" novelty citations. There is no comparable legislative mechanism in New Zealand.

Divisional priority date

AU / NZ Divisional Kats

In Australia, r 3.13D of the Patents Regulations 1991 (Cth) dictates that the priority date of a claim in a divisional application is "the priority date that the claim would have had if the claim was in the earlier specification". The relevant test is an enablement / sufficiency test, i.e., whether the parent application provided a "clear enough and complete enough" disclosure to enable a skilled person to perform the claimed invention without undue burden or further invention. As previously discussed (see IPKat), one also needs to be mindful of restrictions on multiple and partial priorities when claiming added subject matter in a divisional in Australia.

Given it is not possible to add subject matter to divisional applications in New Zealand (and still retain divisional status), the priority date test is the same for divisionals as for their parent applications: is the claim "supported by the matter disclosed in the earlier application"?

Divisional timing

In Australia, a divisional application can be filed at any time while the parent application is pending and, if accepted, within three months of the date of advertisement of acceptance. There is also no limit on the sequential filing of divisional applications, although the Australian Patent Office typically does not look favourably on sequential divisionals that do not seek to either present different claims to the parent application or advance prosecution in any way. In that case, they may deploy mechanisms to advance prosecution.

In New Zealand, the situation is quite different. While there is technically no limit on filing sequential applications, New Zealand imposes a five-year deadline for requesting examination of any and all applications after their filing date, which effectively means that all divisional applications must be filed – and their examination requested – within five years of the parent filing date. This can create complications in New Zealand, where examination timeframes can be slow, and it is often unclear whether a divisional application is necessary before the five-year deadline expires. For this reason, it can be prudent to either request examination early and/or file precautionary divisional applications in New Zealand.

Parent-divisional double patenting

While not historically the case, Australia and New Zealand have aligned in recent years on their approach to parent-divisional double patenting. Essentially, provided the claims are not substantially identical in scope, double patenting does not arise in either jurisdiction. In Australia, the test is where there is "redundancy of claiming" (cf. Smith Kline Beecham p.l.c.'s Application [2000] APO 54). In New Zealand, the test is whether the claims have "substantially the same scope" (cf. Oracle International Corporation [2021] NZIPOPAT 5).

Therefore, both Australia and New Zealand permit claims in a divisional that are broader, narrower or overlap with the claims of its parent application, provided the claims do not have identical scope.

Best method and divisionals

Finally, it would be remiss not to mention the "best method" situation. While Australia and New Zealand are two of the few remaining jurisdictions to retain a best method requirement, the situation in Australia is particularly important for divisional applications. As previously discussed (IPKat), the current state of the law in Australia is that divisional applications must include the best method known to the applicant at the time of filing the divisional application (as a result of the courts determining that the complete specification filing date – at which date the best method must be disclosed – differs from the patent date afforded to divisionals).

It is unlikely a similar situation would (or could) arise in New Zealand, because it is not possible to add subject matter to a divisional application (and because of the ante-dating of divisionals to have the same filing date as the parent).

Concluding remarks

Australia and New Zealand generally offer applicants a good degree of flexibility in relation to the subject matter that can be pursued in divisional applications. While content is key to a successful divisional strategy in Australia, timing tends to be more critical in New Zealand. Interestingly, while New Zealand has relaxed its double patenting requirements in recent years, Australia has tightened its best method requirements. Lobbying efforts are currently underway in both jurisdictions to correct these arguably unreasonable escalations in divisional requirements.