Quick answer: Inter partes review (IPR) and district court litigation are two ways to challenge a patent, and they differ on four things that usually decide the choice. IPR is faster (about 18 months to a decision), cheaper, and uses a lower burden of proof (preponderance of the evidence), but it can only attack validity using prior patents and printed publications, and it carries estoppel that limits what you can argue later in court. District court is slower and costlier and requires clear and convincing evidence to invalidate, but it can hear every defense and can resolve infringement and damages, not just validity.
If you are facing a patent you believe is invalid, or you are deciding how to defend against an infringement claim, one of the earliest strategic questions is where to fight. The two main venues, the Patent Trial and Appeal Board and federal district court, are built for different things. Here is how they compare on the factors that matter most.
What each forum is for
An IPR is a focused validity proceeding at the USPTO. Its only question is whether the challenged claims should survive, judged against prior patents and printed publications. District court litigation is broader. It can decide infringement, validity on any ground, and damages, and it is the only one of the two that can award money or an injunction. So the threshold question is often whether you only need to knock out the patent, or whether you also need a court to resolve infringement and damages.
Speed
IPR is built around a statutory clock. The Board must issue a final written decision within twelve months of institution, and the whole process from petition to decision typically runs about eighteen months. District court patent cases vary widely by district but commonly take two to four years to reach trial, sometimes longer. For a defendant under pressure, that difference alone can be decisive.
Cost
IPR is generally far less expensive than full litigation, though it is not cheap. The current USPTO fees alone start at $23,750 to request review and $28,125 after institution, on top of attorney and expert costs. Even so, a focused IPR usually costs a fraction of taking a patent case through district court discovery and trial, where expenses often climb into the millions.
Burden of proof
This is one of the most important differences. To invalidate a patent in district court, a challenger must prove invalidity by clear and convincing evidence, a high bar. At the PTAB, the petitioner only needs to show unpatentability by a preponderance of the evidence, meaning more likely than not. Since 2018, both forums use the same Phillips claim construction standard, so the burden of proof, rather than how the claims are read, is now the main substantive gap between them.
What you can argue
District court can hear any invalidity theory, including public use, prior sale, indefiniteness, and subject-matter eligibility. IPR is restricted to anticipation and obviousness based on patents and printed publications. If your best invalidity argument is, for example, that the invention was on sale before filing, IPR simply cannot reach it, and federal district court may be the only option.
Estoppel, the catch that surprises people
If an IPR reaches a final written decision, the petitioner is estopped from later raising, in court or at the ITC, any ground it raised or reasonably could have raised in the IPR. In practice that means you may be spending your best prior-art arguments at the PTAB and giving up the right to reuse them in court. This is why the decision to file an IPR is not just about the merits of one proceeding; it shapes what defenses remain available afterward.
The 2025 wrinkle: getting in the door
There is a newer factor that did not weigh as heavily a couple of years ago. Following the 2025 changes to PTAB practice, the Board now denies a substantially larger share of petitions for discretionary reasons, including where a parallel district court case is already well advanced or where the petitioner sat on a known patent for years. That means the existence of a fast-moving court case can itself make an IPR harder to institute, which is something to weigh when the two paths are running in parallel.
So which one?
There is no universal answer, but a few patterns hold. IPR tends to fit when the strongest invalidity argument is prior-art based, speed and cost matter, and the estoppel trade-off is acceptable. District court tends to fit when infringement and damages must be resolved, when the best invalidity defenses fall outside what IPR allows, or when a parallel proceeding makes institution unlikely. Many disputes end up using both, in sequence or together, which makes the timing and estoppel analysis all the more important.
Frequently asked questions
Is IPR cheaper than district court litigation?
Usually, yes. Government IPR fees start at $23,750 to request and $28,125 after institution, and total IPR costs are typically a fraction of full district court litigation, which often runs into the millions through discovery and trial.
Is it easier to invalidate a patent at the PTAB than in court?
The burden is lower at the PTAB, where unpatentability is shown by a preponderance of the evidence rather than the clear and convincing standard used in court. But since 2025 it has become harder to get a petition instituted, so the lower burden only helps once the case is in the door.
What is estoppel in an IPR?
After a final written decision, the petitioner generally cannot later raise, in court or at the ITC, any ground it raised or reasonably could have raised in the IPR. It is a key trade-off of choosing the IPR path.
Strategic forum selection is critical
Choosing the right forum is one of the highest-leverage decisions in a patent dispute. If you are weighing IPR against litigation, our team can map the trade-offs against your 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.
