Post-grant review is the broadest challenge available at the PTAB and the one with the shortest window.
Any ground of invalidity. Subject-matter eligibility, enablement, definiteness, written description, prior public use, on-sale activity — everything inter partes review excludes.
Nine months from issue. After that it is gone permanently.
Which explains why it is used far less than IPR. Most disputes arise years after a patent grants, by which time the only route to the Board is the narrower one.
The core comparison
| Post-grant review | Inter partes review | |
|---|---|---|
| Window | 9 months from issue | After PGR window, or 1 year from service |
| Grounds | Any | §102 and §103 only |
| Evidence | Any | Patents and printed publications only |
| §101 eligibility | Available | Not available |
| §112 enablement / definiteness | Available | Not available |
| Prior public use, on-sale | Available | Not available |
| Institution threshold | More likely than not | Reasonable likelihood |
| Estoppel breadth | Broadest | Broad |
| Timetable | ~18 months | ~18 months |
Grounds and evidence are the whole point of PGR. Everything else about it is similar to or worse than IPR.
§101 availability is the single most cited reason to use it. No other PTAB route permits an Alice-based eligibility challenge. See what can be patented.
Eligibility: which patents qualify
| Patent | PGR available? |
|---|---|
| Effective filing date on or after 16 March 2013 | Yes |
| Earlier effective filing date | No |
| Continuation of a pre-2013 application | Depends on the effective filing date of the claims |
The date reflects the first-inventor-to-file transition. Patents examined under the previous system are outside the procedure, which suppressed PGR use heavily in its early years.
Continuation chains complicate this. A recently issued patent claiming priority to a 2011 application may not qualify, and the answer turns on the effective filing date of the specific claims.
The nine-month window
| Day | Event |
|---|---|
| 0 | Patent issues |
| 0–270 | PGR available |
| 271 onward | PGR gone permanently |
| Any time after | IPR available, subject to its own bar |
Nothing extends the window. It runs from issue, not from when you learned of the patent or when a dispute arose.
Which makes monitoring the prerequisite. A company that only looks at patents when it receives a demand letter will essentially never be inside a PGR window. See patent monitoring.
Watch competitor grants weekly, not quarterly. Nine months sounds generous and is not, once the analysis and drafting time is deducted.
The institution threshold
| Proceeding | Threshold |
|---|---|
| Post-grant review | More likely than not that at least one claim is unpatentable |
| Alternative for PGR | A novel or unsettled legal question important to other patents |
| Inter partes review | Reasonable likelihood of prevailing on at least one claim |
More likely than not is a higher bar than reasonable likelihood, so a petition that would be instituted as an IPR may be denied as a PGR.
The novel legal question route is unusual and real. A petition raising an unsettled question of importance beyond the individual patent can be instituted on that basis, which has no IPR equivalent.
Institution remains discretionary. Rates across PTAB trials generally ran around 65% in October 2024 and about 37% by February 2026 — cite that with its date, since it moves with practice rather than merits. See PTAB discretionary denial.
The estoppel problem
| Post-grant review | Inter partes review | |
|---|---|---|
| Grounds available | All | Documentary §102/§103 |
| Grounds estopped after final decision | All that could have been raised | Documentary grounds only |
| Practical effect | Your entire invalidity case is committed | Documentary case committed |
Because PGR permits everything, it estops everything. A petitioner who receives a final written decision has generally committed every invalidity theory they had or could reasonably have found.
That is a much larger commitment than IPR estoppel. An IPR petitioner keeps §101, §112, prior use and on-sale arguments for court; a PGR petitioner does not.
Which is the central strategic trade. Broader grounds now, in exchange for nothing held back later.
When PGR is worth it
| Situation | PGR? |
|---|---|
| Strong §101 argument, patent recently issued | Yes — no other PTAB route |
| Strong §112 enablement or definiteness argument | Yes |
| Prior public use or on-sale evidence | Yes — unavailable in IPR |
| Documentary prior art only | No — use IPR, keep optionality |
| Patent issued more than 9 months ago | Unavailable |
| Want to preserve court arguments | No |
Documentary-only cases should go to IPR. PGR adds nothing on those grounds and costs far more estoppel.
The clear case for PGR is a ground the Board cannot otherwise hear. A software patent with a serious eligibility problem, caught within nine months, is the textbook example.
Worked example: two patents, two routes
Patent X — issued 4 months ago, software
| Factor | Position |
|---|---|
| Effective filing date | 2019 — PGR eligible |
| Within 9 months | Yes |
| Best ground | §101 — claims recite a result, not a mechanism |
| Documentary prior art | Weak |
| Other grounds held back | None worth preserving |
| Route | Post-grant review |
§101 is unavailable at the Board any other way. With weak documentary art, IPR offered nothing, and the estoppel cost little because there was no strong second theory to preserve.
Patent Y — issued 6 months ago, mechanical
| Factor | Position |
|---|---|
| Within 9 months | Yes — PGR available |
| Best grounds | Two printed publications, strong |
| §101 or §112 arguments | None |
| Prior public use evidence | Possible, not yet developed |
| Route | Inter partes review |
PGR was available and not worth using. The case rested entirely on documentary art, which IPR handles at a lower institution threshold and with narrower estoppel.
The undeveloped prior use evidence sealed it. Filing a PGR would have estopped that argument before it was even investigated.
Procedure
| Stage | Timing |
|---|---|
| Petition filed | Within 9 months of issue |
| Patent owner preliminary response | ~3 months |
| Institution decision | ~6 months from filing |
| Patent owner response, motion to amend | ~3 months after institution |
| Petitioner reply | ~3 months later |
| Oral hearing | ~10–11 months after institution |
| Final written decision | Within 12 months of institution |
| Appeal | Federal Circuit |
The timetable matches inter partes review, which is the one respect in which the two are identical.
Discovery is limited, as in IPR, which is where the cost advantage over district court comes from. See PTAB.
Settlement and termination
| Situation | Effect |
|---|---|
| Settlement before institution | Proceeding typically terminates |
| Settlement after institution | Board may continue to a decision |
| Petitioner withdraws | Board may proceed |
| No final written decision | No estoppel |
The Board can proceed after settlement because the public has an interest in patent validity, though in practice most post-institution settlements do terminate.
No final written decision means no estoppel, which makes early settlement attractive to a petitioner who wants to preserve arguments.
Why it is underused
| Reason | Effect |
|---|---|
| Nine-month window | Most disputes arise too late |
| Eligibility date limit | Excluded older patents for years |
| Broad estoppel | Deters petitioners with multiple theories |
| Higher institution threshold | Riskier petition |
| Requires active monitoring | Most companies do not watch closely enough |
The window is the dominant factor. By the time a company knows a patent threatens it, the nine months have usually passed.
Which makes PGR a monitoring product as much as a litigation one. Using it requires watching competitor grants continuously and being ready to act within months, not years.
Post-grant review: the checklist
- Check the effective filing date. Only patents filed on or after 16 March 2013 are eligible.
- Diarise nine months from issue on any patent you are watching. The window cannot be extended.
- Use it only for grounds unavailable elsewhere — §101, §112, prior use, on-sale.
- Send documentary-only cases to inter partes review, which has a lower threshold and narrower estoppel.
- Price the estoppel seriously. PGR commits your entire invalidity case.
- Meet the higher threshold. More likely than not is harder than reasonable likelihood.
- Consider the novel legal question route where the issue matters beyond the one patent.
- Monitor competitor grants weekly, since nine months is short once analysis and drafting are deducted.
- Do not develop new theories mid-proceeding. Anything you could reasonably have raised is estopped.
- Settle before institution if preserving arguments matters, since no final written decision means no estoppel.