Section 11 of the Patents Act, 1970
Priority dates of claims of a complete specification
Fixes the priority date of each claim in a complete specification, which decides what prior art can be used against that claim.
Official legal text
The verbatim statutory text of this provision is reproduced from the official source and checked by our legal reviewer before it is published here. Until that check is complete for this page, read the exact wording directly from the official source linked below — it is the only version that governs.
Read this as a plain-language summary. If it and the official text, or a relevant Gazette notification, say different things, the official text and the notification are what count.
What this section says, in plain language
Priority is decided claim by claim, not application by application. That single idea is what Section 11 is about. Each claim in a complete specification has its own priority date, and everything published or used before that date can be cited against it, while everything after it generally cannot. Two claims in the same patent can therefore stand on different dates and face different prior art.
The default position is that a claim has the date of filing of the complete specification. The first exception is the provisional specification. Where a claim is fairly based on matter disclosed in a provisional specification filed with the application, that claim takes the date of the provisional. If the complete specification adds subject matter that the provisional never disclosed, claims to that subject matter keep the later date. This is why a thoroughly written provisional is worth the effort, and why a vague one gives an early date to almost nothing.
The second exception covers claims fairly based on matter disclosed in an earlier application by the same applicant, where the later application is filed within the permitted period and the earlier one has not been abandoned or refused in ways the section describes. This is the mechanism that supports divisional applications under Section 16, which take the date of the parent application, and it also underpins the treatment of convention applications filed under Sections 135 and 136 with a priority claim from a convention country.
Where a claim could take more than one priority date under these rules, the earliest of them applies. Section 137 deals expressly with multiple priorities where a complete specification is based on more than one convention application. In practice a single claim in a modern application can trace back to several earlier documents, and the drafting question is whether the earlier documents actually disclose what the claim now covers.
The consequence is very practical. Priority is the single most common battleground in oppositions and revocations, because if a claim loses its early date, prior art from the intervening period becomes usable, and that art is often the applicant's own publication, product launch or conference paper. Assessing a claim's true priority date means reading the earlier document line by line and asking whether it really disclosed what the claim now covers, rather than assuming that filing something early protects everything that came after.
Why this section matters
Applicants relying on provisional filings, convention priority or divisionals, and anyone assessing the validity of a granted claim.
At drafting, at examination when prior art is cited, and in any opposition or revocation where a date is disputed.
The rules that fix each claim's priority date and therefore define the prior art usable against it.
Claims silently lose their early date, and material published in the intervening period becomes citable, often destroying the claim.
How it works in practice
One patent, two priority dates
Ananya Rao files a provisional specification in January describing a water filter cartridge with a layered ceramic membrane. In June she presents the filter at a trade fair in Bengaluru and a trade magazine publishes a detailed article about it. In December she files the complete specification, adding a new self-flushing valve her team developed in August. Claim 1, covering the layered ceramic membrane, is fairly based on the January provisional and takes the January date, so the June article cannot be used against it. Claims 8 to 12, covering the self-flushing valve, were never disclosed in the provisional and take the December date. During examination, the examiner cites the June trade magazine article against claims 8 to 12, and it counts, because the article predates their priority date and describes enough of the surrounding system to matter. Ananya keeps claim 1 but has to narrow the valve claims substantially. Had the August development been captured in a second provisional, the outcome would have been different.
Simplified illustration only. Actual legal outcomes depend on the facts.
Key points to remember
- Each claim has its own priority date; a single patent can carry several.
- The default date is the date of filing of the complete specification.
- A claim fairly based on matter disclosed in a provisional takes the provisional's date.
- Divisional applications under Section 16 take the date of the parent application.
- Convention applications take the date of the corresponding application in the convention country, subject to Sections 135 to 138.
- Where more than one priority date could apply to a claim, the earliest one applies.
- Prior art is judged against the claim's own priority date, not against the application as a whole.
Common mistakes and misunderstandings
- Assuming that filing early protects everything added later. Only claims fairly based on the earlier disclosure get the earlier date.
- Treating priority as a property of the application rather than of each individual claim.
- Publishing or demonstrating an invention between the provisional and the complete specification, and forgetting that the disclosure can be cited against later-added claims.
- Believing a divisional application escapes the parent's prior art. It carries the parent's date and the parent's prior art with it.
Connected provisions
A section of the Act states what the law requires. The detail of complying with it, including forms, periods and office procedure, sits in the Patents Rules, 2003. The Rules are a separate instrument and change far more often, so they are shown alongside rather than folded into the section.
Forms, deadlines and fees
- A convention application in India must be filed within twelve months of the basic application in the convention country to claim its date; check Sections 135 to 138 and the Rules for the exact requirements.
Open the deadline calculator — and have every date confirmed against the current Rules before you rely on it.
The official fee for anything described on this page is set out in the First Schedule to the Patents Rules. It is not the same for every applicant, and it is not the same for online and physical filing, which is why no amount is stated here. How Indian patent fees work.
Related judgments
Case summaries are published only after a qualified reviewer has checked the judgment, the citation and the way the holding is described. Nothing has cleared that review for this provision yet, so nothing is listed here. We would rather show no case note than one that misstates what a court decided. How case notes are prepared.
Questions people ask about Section 11
What is a priority date in a patent application?
The priority date is the date against which the novelty and inventive step of a claim are judged. Anything made available to the public before that date can be cited as prior art against the claim; anything after it generally cannot. Under Section 11 the date is normally the filing date of the complete specification, but a claim fairly based on an earlier provisional specification, an earlier application, or a convention application in another country can take the earlier date instead.
Can different claims in one patent have different priority dates?
Yes, and this is common. Section 11 assigns a priority date to each claim individually. If a complete specification carries some claims that were fully disclosed in the provisional and others covering later improvements, the first set keeps the provisional's date and the second set takes the date of the complete specification. When prior art is cited, each claim is assessed against its own date, which is why validity opinions examine claims one at a time rather than treating the patent as a single block.
What priority date does a divisional application get?
A further application filed under Section 16 takes the date of the original or parent application, which is the point of the mechanism. The divisional cannot include matter that was not disclosed in substance in the parent, so the earlier date is justified by the earlier disclosure. It also means the divisional inherits the parent's prior art landscape. Filing a divisional does not give you a fresh start against documents published after the parent's date but before the divisional was filed.
What does fairly based mean for priority?
It asks whether the earlier document actually disclosed the subject matter now being claimed, in a way a skilled reader would understand as the same invention. A passing mention or an aspirational statement is usually not enough. The assessment is done by comparing the claim with the earlier text, drawings and examples. If the earlier document does not support the claim as it now stands, the claim loses the early date and falls back to the date of the complete specification, with all the prior art that entails.
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