Quick answer: An inter partes review (IPR) is a USPTO proceeding that challenges the validity of an already-issued patent based on prior patents and printed publications. From the petition being filed to a final written decision usually takes about 18 months: the Patent Trial and Appeal Board (PTAB) issues an institution decision within roughly six months of filing, and if the case is instituted, a final written decision follows within twelve months of institution (extendable by up to six months for good cause). The current government fee to request an IPR starts at $23,750 for up to twenty claims.
If you are weighing an inter partes review, the first thing worth understanding is the rhythm of the proceeding. IPR runs on a defined statutory clock, which is one of its main attractions compared with court. Below is the sequence most cases follow, along with the time each stage tends to take and the points where the schedule can shift.
What an IPR actually is
An inter partes review is a trial-style proceeding held at the PTAB (the patent trial and appeal board of the USPTO). A petitioner asks the Board to cancel one or more claims of an issued patent on the ground that the claims are not new (anticipation) or are obvious. Importantly, the challenge can only be based on prior patents and printed publications, not on other validity theories such as a product that was publicly used. That narrow grounds rule is a defining feature of IPR and shapes everything that follows.
Step 1: Confirm the patent is eligible for IPR
Timing matters before anything is filed. For most modern patents, an IPR petition cannot be filed until nine months after the patent issues, or until any post-grant review has finished. There is also a hard deadline working the other way: if the petitioner has been served with a complaint for infringing the patent, the petition generally must be filed within one year of that service. Missing that one-year window is one of the most common ways a strong challenge is lost before it starts.
Step 2: File the petition
The petition is the heart of the case. It identifies each challenged claim, lays out the prior art, and explains, claim by claim, why each one should fall. It is usually supported by an expert declaration. The current USPTO fee to request an IPR is $23,750 for up to twenty claims, with an additional $470 for each claim beyond twenty. A second fee, currently $28,125, applies after institution. These are government fees only and do not include attorney or expert costs.
Step 3: The patent owner responds, and the new discretionary briefing
After the petition is filed, the patent owner may file a preliminary response, generally due within three months. As of 2025, there is also a separate track that did not exist before. The patent owner can now file a standalone brief, typically within two months of the petition, devoted entirely to whether the Board should decline to institute for discretionary reasons. This bifurcated process came out of the March 2025 interim PTAB guidance and has meaningfully changed early strategy, because discretionary denial is now argued on its own schedule rather than buried inside the merits.
Step 4: The institution decision
The Board then decides whether to institute the review. By statute it must do so within three months of the patent owner preliminary response, which lands the institution decision at roughly six months after filing. To institute, the petitioner must show a reasonable likelihood of prevailing on at least one challenged claim. This is also where discretionary denial is resolved. Following the 2025 changes, the Board has been denying a markedly higher share of petitions at this stage, including on newer grounds such as a petitioner having long been aware of the patent, sometimes described as the patent owner settled expectations. Institution is not guaranteed, and the odds now depend heavily on the procedural posture, not just the strength of the prior art.
Step 5: The trial phase
If the case is instituted, it moves into the trial phase: the patent owner files a full response, the petitioner replies, experts are deposed, and the parties may amend or argue claim construction. The PTAB applies the same Phillips claim construction standard the district courts use, a change that took effect in 2018 and removed one of the old gaps between the two forums. A key difference remains on the burden: at the PTAB the petitioner only needs to prove unpatentability by a preponderance of the evidence, a lower bar than the clear and convincing evidence required to invalidate a patent in court.
Step 6: Oral hearing and final written decision
The phase ends with an oral hearing and then a final written decision, which by statute must issue within twelve months of institution, extendable by up to six months for good cause. Add the front-end stages and the typical petition-to-decision span is around eighteen months. The decision can uphold the claims, cancel them, or land somewhere in between. Either side can appeal to the Court of Appeals for the Federal Circuit.
One consequence to plan for: estoppel
A petitioner who gets a final written decision is then estopped from later arguing, in court or at the ITC, any ground it raised or reasonably could have raised in the IPR. That trade-off is central to deciding whether to file at all, and it is covered in more depth in our companion post comparing IPR with district court litigation.
Frequently asked questions
How long does an inter partes review take?
From petition to final written decision is usually about eighteen months. The Board issues its institution decision within roughly six months of filing, and if the review is instituted, the final written decision must come within twelve months, with a possible six-month extension for good cause.
How much does it cost to file an IPR?
The current USPTO request fee is $23,750 for up to twenty claims, plus $470 per additional claim. A post-institution fee, currently $28,125, applies if the review is instituted. Those are government fees only; attorney and expert fees are separate and typically far larger.
When can an IPR be filed?
Generally no earlier than nine months after the patent issues, or after any post-grant review ends. And if the petitioner has been sued for infringing the patent, the petition usually must be filed within one year of being served with that complaint.
What can an IPR be based on?
Only prior patents and printed publications, used to argue that the claims are not new or are obvious. Other validity challenges, such as those based on public use or sale, cannot be raised in an IPR.
Is an IPR easier to win than a court case?
The burden of proof is lower at the PTAB, where unpatentability need only be shown by a preponderance of the evidence, compared with clear and convincing evidence in court. That said, the 2025 changes have made it harder to get a petition instituted in the first place.
If you are considering an inter partes review, either as a challenger or as a patent owner who has been threatened with one, our team works in PTAB proceedings and can walk through the timeline against your specific facts. Reach out through patentlaw.us.
This article is general information, not legal advice, and does not create an attorney-client relationship. Inter partes review rules and PTAB practice change frequently, and recent changes are still evolving, so confirm the current procedures before relying on them.
