An American patent infringement claim is governed by a six-year statute of limitations, but the rules around accrual, continuing infringement, tolling, and defenses like laches can significantly affect timing. This guide explains how the limitations period works, when it starts, and practical considerations for preserving patent rights in U.S. courts.
What Is The Statute Of Limitations For Patent Infringement
The United States imposes a six-year limitations window for patent infringement actions. Under 35 U.S.C. § 286, damages in an action for patent infringement may be recovered only for infringement that occurred within six years before the filing of the complaint. This creates a rolling look-back period, rather than a fixed end date tied to the patent’s grant or expiration.
In practice, this means a plaintiff must file suit within six years of the first act of infringement or risk losing the right to recover damages for earlier acts. This six-year cap does not bar injunctions for ongoing or future infringement, but it limits monetary relief to the prior six years’ worth of infringement.
When Does The Limit Start? Accrual And Ongoing Infringement
The accrual rule for patent infringement generally follows the arrival of a concrete act of infringement in the United States or an ongoing period of infringement. The clock starts when the infringing action first occurs in the U.S. or when the infringement becomes ongoing and known, not at the moment the patent owner discovers the infringement. Once infringement begins, damages can be collected only for six years prior to the filing date.
Important concepts include:
- First act of infringement: The date on which the accused product or process first violates the patent in the United States.
- Ongoing infringement: If infringement continues over time, the patent owner may seek damages for the period within the six-year window preceding the filing, but not for prior periods outside that window.
- Multiple infringers: If multiple parties infringe at different times, each period of infringement is subject to the six-year cap from the respective dates of infringement, as applicable to the plaintiff’s claims.
Continuing Infringement And Damages
Continuing or ongoing infringement can complicate timing. If infringement occurs for several years, the damages period is still limited to six years before the filing date. However, courts may allow remedies for ongoing acts around the time of filing, including potential injunctive relief to stop ongoing infringement. The six-year rule applies to damages, while the court may grant an injunction to prevent further harm from continuing infringement.
Courts consider a defendant’s partial compliance or partial infringement in determining whether the infringement is ongoing and how to frame the damages period. Parties should document dates of known infringements and any communications that began the timeline for potential actions.
Tolling, Discovery, And Equity
Several doctrines can affect when the limitations period runs:
- Tolling: Certain circumstances may toll (pause) the limitations period. For example, a defendant’s concealment of infringement or a court-ordered stay can extend the time to sue. Tolling is fact-specific and often requires evidence of concealment or other equitable considerations.
- Equitable tolling: Courts may apply equitable tolling if the plaintiff acted diligently but was prevented from filing due to extraordinary circumstances. This is not automatic and depends on the facts, including the plaintiff’s diligence and reason for delay.
- Laсhes: Even where statute of limitations has passed, a defendant can argue laches—unreasonable and prejudicial delay in pursuing claims. Laches is an equitable defense and can bar claims if the delay harmed the defendant and the plaintiff slept on rights for an extended period.
Special Considerations And Common Pitfalls
Several practical factors influence when to sue and how to preserve patent rights:
- Joint and several infringers: If there are multiple infringers, the plaintiff must establish infringement against each defendant separately, with timing assessed for each actor.
- Statutory damages vs. injunctions: The six-year limit governs damages, not necessarily the feasibility of an injunction to stop ongoing infringement. Courts may grant an injunction even if the damages window has closed to limit ongoing harm.
- Patent term and expiration: The six-year limitations period operates independently of the patent’s term. A patent nearing expiration does not erase the six-year rule for damages, though the pool of potential damages may be limited by the patent’s life.
- Foreign conduct: Patent infringement occurring outside the United States typically does not trigger U.S. damages under the patent statute, reinforcing the need to focus on the U.S. acts of infringement for accrual and limitations.
Practical Steps To Preserve Rights
To maximize protection under the six-year limit, consider these practical steps:
- Early assessment: Identify and document the first act of infringement in the United States and monitor dates of continuing infringement.
- Timely filing: File suit within six years of the first infringing act to preserve damages for those years within the look-back window.
- Maintenance of records: Keep precise logs of dates, communications, product designs, and distribution channels implicated in infringement.
- Consult counsel early: Patent litigation involves complex accrual, tolling, and laches considerations. Early legal guidance helps tailor strategy to the facts.
- Consider settlements and injunctions: In some cases, pursuing an injunction to halt ongoing infringement can be strategic even when damages are time-barred.
How The Statute Of Limitations Interacts With Other Remedies
Beyond damages and injunctions, patent litigation may involve attorneys’ fees, enhanced damages for willful infringement, and post-issuance reviews. The timing of these remedies often intersects with limitations and tolling rules. For example, willful infringement claims and damages may still be subject to the six-year cap, while certain equitable relief requests can be decided with a broader perspective on ongoing harm.
Summary: Key Takeaways
- Six-year limit: Damages for patent infringement are limited to six years before the filing date.
- Accrual: The clock starts at the first act of infringement in the United States or during ongoing infringement where the act is identifiable and actionable.
- Tolling and laches: Equity can extend or bar claims under specific circumstances; diligence and concealment facts matter.
- Injunctions: Even if damages are time-barred, courts may grant injunctive relief to stop ongoing infringement.