As of 1 May 2023, there has been a substantial change in the manner in which the compliance period for UK divisional patent applications is determined.The compliance period defines the deadline for putting a UK patent application in order for allowance – and if a patent application is not in order for allowance by the end of the compliance period, then it is treated as having been refused. In practice, this can result in patent examiners issuing examination reports in a rapid fire manner as the end of the compliance period approaches and applicants needing to file equally rapid fire responses in order to get an application over the line.The compliance period for an application is calculated as the later of:(i) four years and six months calculated from the earliest priority date of the application; or (ii) twelve months from the date of the first substantive examination report (for the patent family of that patent application). This period can be extended by two months as of right (upon payment of a small fee), but any further extensions to the compliance period are discretionary.The compliance period also sets the deadline for filing divisional applications. This deadline for divisional applications is three months before the end of the compliance period – and extending the compliance period also extends this divisional deadline.Historically, the initial compliance deadline for a divisional application has been set as the compliance period of the parent application from which that divisional is derived. So, if a compliance period was to be extended for a parent application, then any later filed divisional application would commence with this extended compliance period. Therefore, it has been possible to: extend the compliance period of a parent application by two months, file a divisional application with an initial compliance period that is this extended parent compliance period; and then extend the compliance period for that divisional application by another two months. In effect, it has previously been possible to obtain multiple as-of-right extensions to a compliance period by filing divisional applications. This possibility has now been closed.Specifically, as of 1 May 2023, the initial compliance period deadline for a divisional application will be the same as the un-extended compliance period of the parent application.The major effect of this change is that more time pressure will be placed on applicants that file divisional applications towards the end of the compliance period. And it will not be possible to file numerous divisional applications using a cascading strategy. Potentially problematically, this could result in applicants needing to file numerous divisional applications before a resolution has been reached on a parent application. The practical effect of this change is that for applications that disclose multiple inventions a suitable divisional strategy should be considered well ahead of the compliance period to ensure that there is enough time to file these divisional applications and also enough time to progress these divisional applications to grant.Please contact Mathys & Squire if you wish to discuss this change in more detail with a professional representative.