Post-Grant Review: 6 Essential Facts to Know in 2026

A competitor just secured a patent that reads squarely on your product. You have two instincts – wait to be sued, or strike first. A post-grant review is the sharpest early strike the America Invents Act gave you: a proceeding at the Patent Trial and Appeal Board that can cancel a patent’s claims on almost any ground of invalidity. But the window is brutally short, the estoppel is broad, and using it wrong can hand your best arguments to the patent owner. Here is what you need to understand before you file.

What Is a Post-Grant Review?

A post-grant review (PGR) is an administrative trial, created by the America Invents Act and codified at 35 U.S.C. sections 321-329, in which a third party asks the Patent Trial and Appeal Board (PTAB) to cancel one or more claims of an issued patent. Unlike a court case, it is decided by a panel of administrative patent judges at the USPTO, on a faster timeline and under a lower burden of proof – unpatentability by a preponderance of the evidence rather than the clear-and-convincing standard that applies in federal court.

It is one of several ways to challenge a patent without filing a lawsuit. The others – inter partes review and ex parte reexamination – overlap with it but differ sharply in timing and scope. Choosing among them is the first strategic decision.

The 9-Month Window That Makes or Breaks It

The defining feature of this proceeding is timing. A petition must be filed within nine months of the patent’s grant or reissue date. Miss that window and the door closes permanently – your only PTAB option afterward is an inter partes review, which is narrower.

There is a second gate. The review is only available against patents subject to the first-inventor-to-file system, meaning patents with an effective filing date on or after March 16, 2013. Older patents governed by the prior first-to-invent rules cannot be challenged this way at all. Between the short deadline and the eligibility cutoff, the practical takeaway is simple: the moment a threatening patent issues, start the clock. Waiting to see whether you get sued usually means waiting past your best option.

PGR vs Inter Partes Review: Key Differences

The two proceedings are cousins, and picking the wrong one wastes your shot. The differences that matter:

• Timing – a PGR is available only in the first 9 months after grant; inter partes review generally becomes available after that 9-month window closes.
• Grounds – a PGR can raise nearly any invalidity ground, including subject-matter eligibility under section 101 and written-description or enablement defects under section 112. An inter partes review is limited to sections 102 and 103, based only on patents and printed publications.
• Evidence – the broader proceeding lets you use public use, on-sale activity, and other prior art an inter partes review cannot reach.
• Institution threshold – a PGR requires showing it is more likely than not that at least one claim is unpatentable; inter partes review uses a reasonable-likelihood standard.

In short, the earlier proceeding is broader but only briefly available. If your strongest argument is a section 101 eligibility attack or a section 112 defect, and you are inside the nine months, it is the tool built for you.

Grounds You Can Raise at the PTAB

The breadth of available grounds is the reason to act while you still can. A petition can challenge claims on essentially any statutory basis for invalidity:

1. Section 101 – the claims cover ineligible subject matter, such as an abstract idea without an inventive concept.
2. Sections 102 and 103 – the invention is anticipated or obvious, and here you can rely on prior public use or sales, not just documents.
3. Section 112 – the specification fails written description, enablement, or the claims are indefinite.
4. Double patenting and other defects – grounds unavailable in an inter partes review are on the table.

A rigorous patent invalidity search before you draft the petition is what turns a plausible theory into a winning one. Institution is discretionary, and a thin petition gets denied – burning your one clean shot in the process.

The PTAB Process and Timeline

The proceeding runs on a defined schedule, which is part of its appeal for a challenger who wants certainty. After the petition, the patent owner may file a preliminary response, typically within three months. The Board then decides whether to institute the trial.

If it institutes, the parties conduct limited discovery and briefing, and the statute requires a final written decision within one year of institution, extendable by up to six months for good cause. From filing to decision, expect roughly 18 months – far faster than most district-court litigation. That speed, combined with the lower burden of proof, is why accused infringers so often prefer a PTAB challenge to fighting validity in court.

Estoppel: The Strategic Price You Pay

This power comes with a serious catch. If the Board issues a final written decision, the petitioner is estopped from later arguing – before the USPTO, in a district court, or at the ITC – any ground that was raised or reasonably could have been raised during the review.

Because the proceeding lets you raise almost every invalidity ground, that estoppel sweeps far more broadly than the narrower estoppel from an inter partes review. Practically, you may be trading away your ability to relitigate validity later. This is why the decision to file is never just about the strength of one argument; it is about whether you are willing to bet all your invalidity theories on a single 18-month proceeding. A candid opinion of counsel on that trade-off is worth getting before you commit.

Cost and When the Challenge Is Worth It

A post-grant review is not cheap. USPTO petition and post-institution fees run into the tens of thousands of dollars, and rise with the number of claims challenged; attorney and expert fees typically dwarf the government fees. Still, that total is usually a fraction of the cost of defending a full patent-infringement suit.

It is the right tool when a recently issued patent threatens your product, you have a strong eligibility or section 112 argument that an inter partes review cannot reach, and you are inside the nine-month window. If the window has closed, look to inter partes review; if you prefer a lower-profile, lower-cost challenge without estoppel, ex parte reexamination may fit. The worst outcome is doing nothing until a complaint lands and your best proceeding has already expired.

How PerspireIP Can Help

PerspireIP builds the prior-art record and invalidity analysis that a PTAB challenge lives or dies on – and helps you weigh it against inter partes review and reexamination before the nine-month clock runs out. Talk to our patent team about challenging a patent.

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