How to Calculate Patent Expiration for Continuations and Divisionals

Continuation and divisional patents generally expire 20 years from the earliest effective filing date of the original parent application in their continuity chain — not from their own filing date. Under 35 U.S.C. § 120, when an application claims the benefit of an earlier-filed non-provisional application, the 20-year patent term under § 154(a)(2) is measured from that earlier date. This means a continuation filed years after the parent will have fewer remaining years of enforceable patent life at the time it is granted. Understanding this relationship is critical for accurately calculating when any continuation or divisional patent will expire.

Scope: This article covers US utility patents under the 20-year-from-filing regime (applications filed on or after June 8, 1995). All examples assume US law and the current patent term framework.

What Are Continuations and Divisionals?

A continuation application is a new application filed while the parent is still pending, claiming the same invention disclosed in the parent. It allows the applicant to pursue different or broader claims based on the same specification.

A divisional application is filed when the USPTO determines that the original application contains more than one distinct invention (a restriction requirement). The applicant files a divisional to pursue the non-elected invention(s) separately.

Both types claim the benefit of the parent application's filing date under § 120, which is what ties their patent term to the parent's filing date.

How 35 U.S.C. § 120 Affects Patent Term

Section 120 allows a later-filed application to claim the benefit of an earlier-filed application's filing date for prior art purposes. However, this benefit comes with a cost: under § 154(a)(2), the patent term is measured from “the date on which the application for the patent was filed in the United States or, if the application contains a specific reference to an earlier filed application or applications under section 120, 121, 365(c), or 386(c), from the date on which the earliest such application was filed.”

In practice, this means the 20-year clock starts from the oldest application in the chain — even if the continuation was filed much later.

Which Relationship Types Affect Patent Term?

• Continuation (CON): Yes — the term traces back to the parent's filing date.
• Divisional (DIV): Yes — same as continuations, the term traces back to the parent.
• Continuation-in-Part (CIP): Yes, but with nuances. The term traces back to the parent for subject matter disclosed in the parent. New matter added in the CIP may receive a different effective date for patentability purposes, but the patent term is still measured from the earliest parent filing date. See CIP nuances below.
• Provisional (PRO): No — provisional applications are explicitly excluded from the patent term calculation under § 154(a)(2). A provisional filing date does not pull back the 20-year clock.

How to Trace the Continuity Chain

1. Start with the patent in question and look up its application data sheet or the front page of the patent, which lists related applications.
2. Identify the parent application(s) referenced under § 120, 121, or 365(c).
3. For each parent, repeat the process: check whether that application also claims benefit of an even earlier application.
4. Continue until you reach an application that does not claim benefit of any earlier non-provisional application. That application's filing date is the earliest effective filing date.
5. Ignore any provisional application in the chain — it does not affect the 20-year term.

For a detailed walkthrough, see our guide on finding the earliest effective filing date.

Worked Example: A Continuation Filed in 2018 from a Parent Filed in 2014

National Stage Entries (PCT to US)

When a patent application enters the US national stage under 35 U.S.C. § 371, the international filing date (PCT filing date) is treated as the US filing date for patent term purposes. If the PCT application itself claims the benefit of an earlier US non-provisional application, the term traces back to that earlier filing date.

Foreign priority claims (under the Paris Convention or § 119) do not affect the 20-year patent term. A US national stage application claiming Paris Convention priority from a foreign application filed a year earlier still has its 20-year term measured from its own international (PCT) filing date.

CIP Nuances

A continuation-in-part (CIP) includes new matter not disclosed in the parent. For patent term purposes, the 20-year clock still runs from the earliest parent filing date in the chain, regardless of whether specific claims rely on new matter. However, for prior art purposes, claims directed to new matter may only be entitled to the CIP's own filing date. This distinction is important for validity analysis but does not change the patent term calculation.

Common Mistakes

• Using the continuation's own filing date. The most common error. The 20-year term runs from the earliest parent, not the continuation's filing date.
• Including provisionals in the chain. Provisionals do not affect term. Only non-provisional applications count.
• Ignoring national stage dates. For PCT applications, the international filing date is the relevant date.
• Assuming all CIP claims get the parent's priority date. New matter claims may have a later effective date for prior art, even though the term is the same.

Last reviewed: April 2026

Legal disclaimer: This article is for informational purposes only and does not constitute legal advice. Consult a registered patent attorney or agent for advice specific to your situation. patentreply.ai is not a law firm.