Expired Patents

How Patents Expire and Lapse - the Legal Implications

It is generally known that patents allow the owner exclusive rights to exploit an innovation. However, the period of that protection is limited. There is a basic quid pro quo that underlies US patent law: if you develop a new and useful invention, you can have exclusive rights to that invention for a defined time period, but then it enters the public domain and anyone can use it to their benefit. Many people do not understand this bargain or that the patented technology is free to use after a patent expires. Entrepreneurs and technologists can analyze expired patents to adopt, adapt, or build upon the underlying invention without paying licensing fees.

Lapsed patents work differently. A utility patent can lapse due to a failure to pay required patent maintenance fees. The public can lawfully use the technology in a lapsed patent. However, if the patent lapsed due to inadvertent failure to pay the maintenance fees, the patent owner may later revive the patent. Thus, practicing the invention of a lapsed patent carries some risk and should be considered with the guidance of a skilled patent attorney.

In this article, we discuss legal framework of expired and lapsed patents and the legal issues related to utilizing the formerly patented technology.

What Does It Mean When a Patent Expires?

When a patent expires, the exclusive rights granted to the patent owner, including the right to exclude others from making, using, or selling the invention, come to an end. At that point, the intellectual property becomes part of the public domain, and anyone can use it without fear of infringement.

Uninformed entrepreneurs (e.g., inventors, small businesses, etc.) may miss out on valuable opportunities by overlooking the benefits of using expired patents. For example, if a consumer electronics patent from 20 years ago has expired, you may be able to use its original invention as a foundation for further innovation, saving time and R&D costs.

In the United States, patents are governed by federal patent law and administered through the United States Patent and Trademark Office (USPTO). The USPTO has a public patent database of all issued patents that allows anyone to find patented technology relevant to their business or field. You can search by keyword, inventor name, patent number, assignee, or filing date. Once you locate a patent, PDF or image files of the patent are viewable. To determine whether the patent has expired, you can look at the filing date, issue (grant) date, and the type of patent (utility, design, or plant) on the first page of the patent. For utility patents filed after June 8, 1995, the term is generally 20 years from the filing date. However, there are some nuances to determining the filing date.

How to Determine the Effective Filing Date

Accurately identifying the effective filing date is required to determine the patent's term and expiration date. To determine the effective filing date of a utility patent from the first page of the patent document, which includes various data sections identified by Internationally Agreed Numbers for the Identification of Data (INID codes), found in parentheses on the left side of each column. If the patent was the result of a single application with no claims to prior filed provisional or parent applications, the patent term will be determined based on the filing date of the application. The “Filed” field (22) found in the first column of the first page provides the date on which the application was filed. However, if the patent claims benefit of an earlier non-provisional patent application (e.g., a parent application), the effective filing date will be the date of the earliest validly claimed non-provisional patent application listed in the “Related U.S. Application Data” section (63).

Related Patent Applications and Priority Claims

If a patent claims priority to any prior non-provisional patent filings, the “Related U.S. Application Data” section lists the any continuation, continuations-in-part, and/or divisional priority claims, along with the corresponding filing dates. The effective filing date is the earliest date on which the subject matter claimed in the patent was first disclosed in an earlier non-provisional patent application to which the patent validly claims priority.

Chains of Patents in a Patent Family

When a patent lists only priority claims to divisional and/or continuation patents in the “Related U.S. Application Data” section, the effective filing date is generally the earliest filing date in that chain (see the image below), assuming the claims are fully supported by the original disclosure. If the list includes a priority claim to a continuation-in-part (CIP), the effective filing date for each claim depends on whether it is supported by the earlier application. Claims supported by the original parent application (earliest filed non-provisional) retain the parent’s date; new matter introduced in the CIP gets the CIP’s filing date. Determining the correct date may require reviewing the specifications of all listed applications.

Provisional Priority Claims

Section (60) identifies any priority claims to provisional patent applications. However, these priority claims do not impact the 20 year patent term. They are irrelevant to determining when the patent expiration date.

Foreign Priority Claims

Foreign priority claims under 35 U.S.C. § 119 do not affect the patent term in the United States. While they establish an earlier priority date for determining novelty and non-obviousness, the patent term is still calculated from the actual U.S. filing date of the non-provisional application, not the foreign priority date. Foreign priority can strengthen patent validity by reducing the amount of available prior art, it does not shorten or extend the statutory patent term in the U.S.

Patent Term Extensions and Adjustments

Any Patent Term Adjustment (PTA) or Patent Term Extension (PTE) granted for a patent is typically noted in the “Notice” section on the first page of the issued patent. However, these two extensions arise under different statutes, serve different purposes, and apply under different circumstances.

Patent Term Adjustment, governed by 35 U.S.C. § 154(b), compensates for delays caused by the USPTO during prosecution. This includes delays such as extended examination, failure to meet response deadlines, or time spent in appeal. The adjustment is automatically calculated and expressed as a number of days added to the standard 20-year term from the earliest effective filing date of a utility patent. PTA applies only to utility patents, not design or plant patents.

Patent Term Extension (PTE) is granted under 35 U.S.C. § 156 and applies to patents covering products subject to regulatory review, such as pharmaceuticals, medical devices, and agricultural chemicals. PTE compensates for the time lost while waiting for FDA or other regulatory approval before a product can be marketed. PTE is granted upon request, and if awarded, the extension is noted on the face of the patent, often with language such as “180-day patent term extension granted.”

Both PTA and PTE extend the enforceable life of the patent beyond the standard term, but they are based on different causes of delay, administrative delays for PTA and regulatory delays for PTE, and are authorized by separate statutory provisions.

Terminal Disclaimers

A terminal disclaimer is a legal statement filed with the USPTO in which a patent applicant agrees to limit the term of a later-filed patent so it expires no later than an earlier related patent, often in the same patent family. This is typically done to overcome a non-statutory double patenting rejection, where two patents claim obvious variations of the same underlying invention. The terminal disclaimer ensures that the public does not suffer from extended patent protection for obvious variants of the same invention.

Terminal disclaimers affect the patent’s term by cutting it short, aligning its expiration with the earlier patent's expiration date. Importantly, terminal disclaimers also require that the patents remain commonly owned. If ownership is later divided, the disclaimed patent may become unenforceable.

This principle was confirmed in In re Hubbell, 709 F.3d 1140 (Fed. Cir. 2013), where the Federal Circuit upheld the requirement for common ownership of patents subject to a terminal disclaimer. The court emphasized that separating ownership undermines the basis for the disclaimer, preventing unjustified time extensions of exclusive rights. Thus, a patent holder should carefully manage licensing agreements and assignments in families with terminal disclaimers to avoid unenforceability of valuable patent assets.

Patent Cooperation Treaty - US National Stage: a Special Case

The patent term of a U.S. national stage application filed under 35 U.S.C. § 371, based on an international Patent Cooperation Treaty application (PCT), is generally 20 years from the international filing date of the PCT application, not the date of national stage entry. The same term calculation is applied to national stage applications as to regular U.S. utility applications using the PCT application date as the priority date. Therefore, even if national stage entry occurs up to 30 months later, the 20-year term still begins from the PCT’s international filing date. If the PCT application claims priority to an earlier foreign patent application under 35 U.S.C. § 119, that foreign priority date does not affect the term, it only affects patentability. Additionally, PTA and PTE are applicable and may extend the term.

Figuring Out Patent Expiration - You May Need the Assistance of a Patent Attorney

Determining a patent’s expiration requires careful consideration of its priority dates, any patent term extensions (PTEs), and the presence of terminal disclaimers. The priority date, often the earliest effective filing date listed in the “Related U.S. Application Data” section, establishes the starting point for calculating the standard 20-year term for utility patents. Any granted PTE adds days to this term to compensate for USPTO or regulatory delays. However, a terminal disclaimer can override the calculated term by shortening it to match the expiration of an earlier related patent. When a terminal disclaimer is present, determining the correct expiration date may require reviewing the file wrapper (the patent’s prosecution history) to identify the prior patent to which the disclaimer is tied and whether that earlier patent remains enforceable. Without this context, expiration dates on the face of the patent may be misleading. Therefore, analyzing all of these elements together is essential for accurately assessing a patent’s term.

Multiple Ways a Patent Can Expire or Lapse

Although patents are granted for a specific term, they can expire early or lapse for a variety of reasons. Understanding the different pathways to expiration is essential for entrepreneurs that plan to use, license, or build upon a technology patented by someone else, and for the patent holder themselves. Misinterpreting a patent’s status can lead to legal risks or missed opportunities for either kind of party. Below are several common scenarios that may lead to early expiration or lapse of intellectual property rights.

Natural Expiration

A patent naturally expires when it reaches the end of its statutory term, which is typically 20 years from the earliest effective filing date. Once this term expires, the patent owner no longer has the exclusive rights to prevent others from making, using, or selling the invention. At that point, the patented technology enters the public domain, where it may be freely used by competitors and the public. Natural expiration is the most straightforward method by which a patent ends. However, it is quite common for the filing and prosecution history of the patent to be more complicated. In such circumstances, close attention must be paid to filing dates, patent term extensions, and other factors to calculate accurately. Businesses analyzing expired patents should always verify the correct term based on the type of patent and applicable rules.

Failure to Pay Maintenance Fees

For utility patents, the patent office requires the patent holder to pay maintenance fees at 3.5, 7.5, and 11.5 years after the patent is granted. Failure to make timely payments causes the patent to lapse and become unenforceable. However, the USPTO provides a six-month grace period during which the patent owner can reinstate the patent by paying the overdue fee along with a surcharge. If the owner fails to take action within that time, the patent will be considered lapsed. However, even if a patent lapses, it may still be reinstated under certain conditions, which can complicate determinations of enforceability. If the patent lapsed due to inadvertent error, it can be revived. Businesses considering use of lapsed patents should consult with patent attorneys to assess the risk that the patent holder will revive the patent and whether intervening rights may apply to safeguard their activities.

Terminal Disclaimer Results in Early Expiration

A terminal disclaimer is filed to overcome a non-statutory double patenting rejection by aligning the term of one patent with that of an earlier related patent in the same family. When this occurs, the disclaimed patent will expire no later than the earlier patent’s expiration date, even if it would otherwise qualify for a longer term. This can significantly shorten the duration of patent protection. Terminal disclaimers also require that both patents remain commonly owned for enforceability. If the patents become separately owned through sale, transfer, or licensing, the disclaimed patent may become unenforceable, as clarified by Federal Circuit case law such as In re Hubbell. To accurately determine expiration, especially in complex families, it may be necessary to review the file wrapper and identify which patent the terminal disclaimer references. Overlooking a terminal disclaimer can result in relying on a patent that has already expired.

Court Rulings

A patent can also cease to be enforceable through judicial invalidation. U.S. federal courts, including the Supreme Court, may declare a patent invalid or unenforceable for several reasons, including lack of novelty, obviousness, failure to meet written description requirements, or inequitable conduct during prosecution. When a patent is invalidated by court ruling, it is as if the legal right never existed. This outcome applies retroactively and can affect licensing agreements, infringement lawsuits, and business strategies built around the patent. Companies relying on active patents, especially in competitive fields like consumer electronics, pharmaceutical patents, and power systems, should stay informed about relevant litigation that may impact the enforceability of key patent assets. It is important to note that a patent listed as active in the USPTO database may still have been nullified by court action, so legal status checks should always include a litigation search.

Legislative Changes

In rare but impactful cases, changes in patent law or regulatory exclusivity rules can affect whether a patent remains enforceable or how long its term lasts. This is particularly relevant to pharmaceutical patents and biologics, where legislation such as the Hatch-Waxman Act or the Biologics Price Competition and Innovation Act (BPCIA) may shorten or extend effective exclusivity periods. Additionally, international treaties and domestic reforms may alter how patent terms are calculated or whether international protection is available. Some reforms have introduced patent term adjustments (PTAs) or eliminated extensions under certain circumstances. Businesses should monitor legislative developments to assess how they might impact patent strategy, particularly for products reliant on extended exclusivity for market entry or licensing revenue. Consulting with experienced patent attorneys is critical to understanding how evolving rules may affect the enforceability or term of a particular patent portfolio.

What Happens After Patent Expiration?

Once a patent expires, it enters the public domain, meaning the exclusive rights previously held by the patent owner no longer apply. For large and small businesses alike, this opens the door to using the underlying invention for product development, manufacturing processes, or commercialization without needing a license or worrying about infringement claims. Expired patents serve as a rich source of technical knowledge and proven designs, making them valuable tools for businesses looking to further innovation with reduced legal risk and lower R&D investment.

Practice of Expired Patents

The expiration of a patent is in the public domain: anyone is legally free to use, make, sell, or improve upon the previously protected invention without obtaining permission or paying licensing fees. This allows new market entrants to build upon old patents, especially in industries like consumer electronics, manufacturing, and pharmaceuticals. For instance, when pharmaceutical patents expire, generic manufacturers can produce equivalent drugs at lower costs, often resulting in increased accessibility for consumers and new business opportunities for manufacturers. In other industries, expired patents can form the basis for product lines, reduce development timelines, or inspire entirely new solutions. Reviewing and analyzing expired patents can give businesses a competitive edge while fostering innovation.

What Happens After a Patent Lapses for Failure to Pay Maintenance Fees?

Lapsed patents may not be permanently unenforceable. In some cases, a patent holder can reinstate a lapsed utility patent by paying overdue maintenance fees within the USPTO’s six-month grace period. In limited circumstances, reinstatement may also be granted beyond that period through a successful petition showing that the lapse was unintentional. When a patent is reinstated, it regains enforceability, but not without consequences for third parties.

If a business began using the invention during the lapse in good faith, it may acquire intervening rights under patent law. These rights can shield the user from infringement liability, particularly for products made, purchased, or developed while the patent was unenforceable.

What Are Intervening Rights?

Intervening rights are statutory defenses available to third parties who, in good faith, begin using, making, or selling a patented invention during a period when the patent is unenforceable, such as after lapse due to nonpayment of maintenance fees or after a substantial amendment to claims in a reissue or reexamination proceeding. These rights are codified in 35 U.S.C. § 41(c). While often discussed in the context of post-grant proceedings, courts have extended these principles to lapsed and later-reinstated patents.

There are two categories of intervening rights:

Absolute Intervening Rights:

Absolute rights allow a third party to continue using or selling specific products that were made, purchased, or contracted for before the patent was reinstated. These rights are not discretionary, they are granted as a matter of law if the activity was initiated in reliance on the patent’s lapse.

Equitable Intervening Rights:

Equitable rights give courts discretion to permit continued activity, potentially including expansion of use, based on fairness and the extent of investment or reliance made during the lapse. Courts weigh factors such as the nature of investments, duration of use, and knowledge of the original patent.

Courts may apply equitable doctrines, including estoppel and reliance-based protections, to shield third parties who acted in good faith during the lapse. Therefore, while § 41(c) permits reinstatement, it does not erase the legal significance of a period during which the patent was unenforceable. Businesses relying on such a lapse should consult with patent attorneys to assess whether they have a viable intervening rights defense if the patent is later reinstated.

Plant Patents and Design Patents

The term of a patent also varies depending on the type of patent granted. Utility patents, which cover new and useful processes, machines, or compositions of matter, generally last 20 years from the earliest effective filing date under 35 U.S.C. § 154(a)(2).

In contrast, plant patents, which protect asexually reproduced plant varieties, also have a 20-year term, but unlike utility patents, no maintenance fees are required to keep them in force. Thus, there is no opportunity for lapsed plant patent.

Design patents, which protect the ornamental design of a functional item, have a different term entirely. For applications filed on or after May 13, 2015, the term is 15 years from the grant date under 35 U.S.C. § 173, and likewise require no maintenance fees. Understanding these differences is essential when evaluating a patent’s duration.

Conclusion

When a patent expires, it opens the door for use of the patented technology and further innovation, allowing others to use, build upon, and earn money from the original invention without needing to negotiate licensing agreements. However, it’s crucial to accurately determine the patent expiration date. Missteps can lead to costly litigation or lost opportunities.

By working with patent attorneys, you can analyze expired patents in your field, stay ahead of your competitors, and turn intellectual property rights once held by others into growth opportunities for your business.

To learn more or get help with evaluating expired patents, contact us for a consultation with an experienced patent attorney.

© 2025 Sierra IP Law, PC. The information provided herein does not constitute legal advice, but merely conveys general information that may be beneficial to the public, and should not be viewed as a substitute for legal consultation in a particular case.