The Two Flavors of Invalidation: IPR vs. PGR

Last Updated: June 20, 2026 by SK Pulse Editorial Team

Both Inter Partes Review (IPR) and Post-Grant Review (PGR) are trial proceedings conducted before a panel of three Administrative Patent Judges (APJs) at the Patent Trial and Appeal Board (PTAB). Unlike a random jury drawn from the local DMV line, these judges actually have deep technical and legal backgrounds. If your patent relies on pseudo-scientific jargon to mask a lack of innovation, they will know. However, while they share the same tribunal, these two proceedings have entirely different rules of engagement.

To navigate the PTAB effectively, you must understand the distinct tactical differences between the “Kitchen Sink” and the “Sniper Rifle.”

The Strategic Breakdown: IPR vs. PGR

Tactical Feature	Post-Grant Review (PGR)	Inter Partes Review (IPR)
Timing Window	First 9 months immediately following patent issuance.	After the initial 9-month window closes.
Grounds for Attack	Broad: § 101, § 102, § 103, § 112 (Any statutory invalidity ground).	Narrow: Only § 102 and § 103.
Evidence Allowed	Patents, printed publications, prior use, sales, expert testimony on eligibility.	Strictly patents and printed publications only.
Estoppel Risk	High: Barred from raising anything you “reasonably could have raised.”	Moderate: Limited to publication-based prior art.
USPTO Base Fee	~$47,500 (Filing + Post-Institution)	~$41,500 (Filing + Post-Institution)

1. Timing is Everything

• PGR: This is the early-bird special. Governed by 35 U.S.C. § 321, you must file a PGR petition within the first 9 months after a patent is issued or reissued.
• IPR: This is the long game. Under 35 U.S.C. § 311, you generally cannot file an IPR until the 9-month PGR window has slammed shut.

⚠️ The 1-Year Litigation Trap: If you are sued for patent infringement in federal district court, you have exactly one year from the date you are served the complaint to file your IPR petition. Miss that strict deadline, and the PTAB doors are locked forever.

2. Grounds for Attack

• PGR (The Kitchen Sink): PGRs are exceptionally broad. You can attack a patent on virtually any statutory ground. Is it not novel (102)? Is it obvious (103)? Is it an abstract idea pretending to be software (101)? Did the inventor fail to actually describe how to build the thing (112)? You can throw it all at the wall here.
• IPR (The Sniper Rifle): IPRs are strictly limited. You can only challenge the patent based on novelty (102) and obviousness (103), and your evidence is entirely restricted to prior art consisting of patents and printed publications. You cannot argue that the invention is an ineligible abstract concept, nor can you bring in a physical prototype as prior art.

3. The Trap of Estoppel

Estoppel is the legal system’s way of saying, “Speak now or forever hold your peace.” If the PTAB issues a Final Written Decision, you are barred from raising those same invalidity arguments in future district court or ITC proceedings.

• PGR Estoppel: Terrifyingly broad. You are barred from raising any ground you raised or “reasonably could have raised.” Because PGR allows for almost any invalidity argument, losing a PGR effectively strips you of most of your defenses in federal court.
• IPR Estoppel: Narrower, simply because you are statutorily limited to raising only 102 and 103 challenges based on printed publications.

4. The Price Tag

The PTAB is billed as a “cheaper” alternative to district court litigation. That is true, but only in the way that buying a Porsche is cheaper than buying a private jet. A PGR requires a $20,000 filing fee and a $27,500 post-institution fee. An IPR costs $19,000 to file and $22,500 if instituted. And that is just what you pay the government—factor in expert witnesses and specialized attorney fees, and you are easily looking at hundreds of thousands of dollars.

💡 Forecast Your USPTO Litigation Budget: The PTAB is ruthlessly expensive. Before launching an IPR or PGR, you must forecast your financial runway. Model your base USPTO filing, maintenance, and procedural fees using our interactive tool:

Launch the U.S. Patent Filing & Maintenance Fee Estimator (Interactive Calculator)

The Ultimate Showdown: PTAB vs. District Court

Why do challengers rush to the PTAB when they are already fighting in district court? Because the deck is heavily stacked in their favor. At the PTAB, claims are evaluated under a lower burden of proof (“preponderance of the evidence”) rather than the strict “clear and convincing evidence” standard required by federal courts. Because these paths run parallel, defendants immediately ask the district court to pause (stay) the infringement lawsuit while the PTAB does its dirty work. If the PTAB kills the patent, the multi-million-dollar court case simply evaporates.

The 2025–2026 Reality Check: A Statistical Bloodbath

If you are a patent holder, the latest statistics might give you a mild panic attack, followed by a strange sense of relief, followed by another panic attack. IPRs continue to absolutely dominate the landscape, accounting for about 95% of all PTAB petitions, with PGRs hovering around 5%. But the real story of the last couple of years is the wild swing in institution rates.

The Rise of the Discretionary Denial

The PTAB does not have to hear your case. The USPTO Director has the discretion to deny a petition, often because a parallel district court trial is moving too fast and the PTAB doesn’t want to duplicate efforts.

Over the course of 2025 and into 2026, under changing USPTO leadership, the use of these “discretionary denials” skyrocketed. In 2024, the institution rate (the percentage of petitions the PTAB agreed to hear) sat at a comfortable 68%. By early 2026, that overall institution rate had plummeted to around 37%. If you are a patent holder, this sounds like great news. The “Death Squad” is taking fewer cases! But do not pop the champagne just yet.

The Kill Rate Remains Brutal

If the PTAB does institute your trial, they are coming for blood. Recent data from late 2025 and early 2026 shows that when the PTAB issues a Final Written Decision, they cancel an astonishing 76.5% of all instituted claims. In nearly 60% of those decisions, every single instituted claim was wiped off the face of the earth. Less than a quarter of instituted claims survived the ordeal unscathed. In short: The bouncer at the door of the PTAB has gotten incredibly strict about who they let into the club. But once you are inside, the mortality rate hasn’t changed a bit.

The Cynical Bottom Line

The modern patent litigation ecosystem operates on a simple, ruthless premise: grant the patent easily, but make it wildly expensive to defend. For challengers, the PTAB remains the ultimate weapon of mass destruction. Sure, you might have to file your petition early and pray you don’t get slapped with a discretionary denial, but spending $400,000 at the PTAB to completely vaporize a plaintiff’s patent is infinitely better than spending $5 million in federal court arguing in front of a layperson jury that thinks “Java” is just a type of coffee. For patent owners, your beautiful, gold-sealed certificate from the USPTO is ultimately just an invitation to a high-stakes knife fight in Alexandria, Virginia. May the odds—and the Administrative Patent Judges—be ever in your favor.

About the Author & Editorial Policy

SK Pulse Editorial provides operational, practitioner-grade intelligence for global tech founders, venture-backed startups, and IP litigation managers. The author is a patent law professional coordinating directly with licensed U.S. patent attorneys, but is not a licensed patent attorney, registered patent agent, or legal counsel.

Disclaimer: This article constitutes editorial analysis and is for informational and educational purposes only. It does not constitute formal legal advice or establish an attorney-client relationship. U.S. Patent law, AIA provisions governing PTAB trials (IPR and PGR), and estoppel rules are highly complex and continuously evolving. All IP litigation strategies, especially those involving parallel district court stays and statutory time bars, should be made in direct consultation with a qualified, licensed intellectual property litigator.