What a priority claim does
A priority claim allows a later patent application to use an earlier filing's date as its effective filing date for prior art purposes. Under the AIA first-inventor-to-file system, the 'effective filing date' determines what counts as prior art under § 102. An earlier effective filing date means more prior art is excluded — competitor filings, public disclosures, and publications that occurred after the priority date cannot be used against claims that properly claim priority to that earlier date. Priority claims are therefore a core tool in patent prosecution strategy: file early (even provisionally) to establish an early prior art cutoff, then prosecute the full application within the relevant priority window.
Domestic priority: provisionals (§ 119(e))
35 U.S.C. § 119(e) allows a non-provisional patent application to claim the benefit of a US provisional application's filing date. Requirements: the non-provisional must be filed within 12 months of the provisional; the priority claim must be made in the application data sheet (ADS) or the specification's first paragraph; and the provisional must adequately disclose the subject matter for which priority is claimed (the written description and enablement requirements apply). For claims in the non-provisional that cover subject matter not in the provisional, the non-provisional's own filing date is the effective filing date. Multiple provisionals can be claimed by a single non-provisional as long as all were filed within 12 months before the non-provisional.
Domestic priority: continuations (§ 120)
35 U.S.C. § 120 allows continuation, divisional, and continuation-in-part (CIP) applications to claim the benefit of a parent US non-provisional's filing date. Unlike provisional priority (which has a 12-month absolute limit), § 120 priority requires only that the continuation/divisional be copending with the parent — filed before the parent issues or is abandoned. Continuation claims are entitled to the parent's priority date for all subject matter adequately disclosed in the parent specification. CIP applications receive the parent's priority date only for subject matter disclosed in the parent; new matter added in the CIP uses the CIP's filing date. The chain of priority through a continuation family is only as strong as its weakest link — each application in the chain must claim priority to the previous one, and the chain must remain copending throughout.
International priority: Paris Convention (§ 119(a)-(d))
The Paris Convention gives applicants 12 months from their first national filing in any member country to file in other member countries and claim the first filing's date as priority. The US implements this in 35 U.S.C. § 119(a)-(d): a US application claiming Paris Convention priority from a foreign application must be filed within 12 months of the foreign filing, identify the foreign application in the ADS or specification, and the claimed invention must be for the same subject matter as the foreign application. Paris Convention priority prevents intervening prior art from being used against the US application for disclosed subject matter. The Paris Convention is the foundation of international patent filing strategy — a startup filing in one country first can use that first filing's date as the priority date in all 175+ Paris Convention member countries.
PCT applications and priority
A PCT (Patent Cooperation Treaty) application can claim priority from an earlier national application (US provisional, US non-provisional, or foreign national filing) under the Paris Convention. The PCT application then serves as an international filing that can enter national phases in 150+ countries within 30 months of the priority date. The priority date must be the PCT application's earliest claimed priority date — if claiming from a US provisional, the PCT must be filed within 12 months of the provisional. Example: file US provisional (Year 1, Day 0) → file PCT claiming provisional priority (Year 1, Day 365) → national phase entry in target countries (Year 3, Day 0, i.e., 30 months from the provisional). The PCT application preserves the provisional priority date throughout all national phases, as long as the PCT adequately discloses the subject matter claimed in each national phase application.
Effective filing date under AIA
Under the AIA (America Invents Act), the effective filing date of a claimed invention is the earliest filing date of any application to which the application claims priority, for subject matter adequately disclosed in that earlier application. This concept of effective filing date replaced the pre-AIA concept of 'date of invention' (which allowed inventors to antedate prior art by proving an earlier actual invention date). Under AIA, there is no 'swearing behind' prior art by proving an earlier invention date — the priority claim chain determines the prior art cutoff. The AIA effective filing date standard also changed how interferences became derivation proceedings — rather than deciding who invented first, the AIA system looks at who filed first (with priority claims determining the effective filing date of each party's claims).
Frequently Asked Questions
What is a priority claim in patent law?
A priority claim allows a patent application to benefit from the filing date of an earlier application. Instead of using the later application's actual filing date as the prior art cutoff, the later application uses the earlier ('priority') application's filing date. This matters because prior art is measured relative to the effective filing date — anything publicly known before that date can be prior art. A priority claim to an earlier filing date moves the prior art cutoff back, potentially excluding competitor filings and publications that occurred between the priority date and the actual filing date of the later application. Priority claims can be domestic (within the US, e.g., claiming benefit of a provisional application) or international (under the Paris Convention, claiming priority from a foreign application).
How do I claim priority to a provisional patent application?
To claim priority to a provisional patent application, the non-provisional application must: (1) be filed within 12 months of the provisional application's filing date; (2) include a specific claim for benefit under 35 U.S.C. § 119(e) in the application data sheet or in the specification; and (3) identify the provisional application by its serial number. The priority claim must be made in the non-provisional application — it cannot be added later without a petition (and potentially additional fees and showings) if the 12-month deadline has passed. The provisional must adequately disclose the claimed subject matter for the non-provisional to benefit from the provisional's priority date for those claims. Claims in the non-provisional that cover subject matter not disclosed in the provisional use the non-provisional's filing date as their effective filing date.
How does Paris Convention priority work?
The Paris Convention for the Protection of Industrial Property allows patent applicants to file in any member country within 12 months of their first national filing and claim the benefit of the first filing's date as the priority date. For example, a startup that files a US provisional in January 2024 can file a PCT application or direct national applications in Europe, Japan, and other Paris Convention countries by January 2025 and claim the provisional's January 2024 priority date. This means competitor filings and publications that appeared between January 2024 and January 2025 cannot be used as prior art against those foreign applications (for subject matter disclosed in the original application). The Paris Convention priority window is strictly 12 months for patents (6 months for designs and trademarks). The United States is a Paris Convention member; the system covers over 175 countries.
What is the difference between domestic and foreign priority?
Domestic priority refers to priority claims within the US patent system: (1) § 119(e) priority — a non-provisional claiming benefit of a US provisional (12-month window); (2) § 120 priority — a continuation or divisional application claiming the benefit of a parent US non-provisional (no time limit — the continuation must be copending with the parent); (3) § 121 divisional priority — a divisional resulting from a restriction requirement, with special ODP safe harbor protections. Foreign priority refers to priority claims from applications filed in other countries: (1) § 119(a)-(d) priority — US application claiming benefit of a foreign national application (12-month Paris Convention window, must be the first filing); (2) § 365 — US national phase entry claiming the PCT application's priority date. The key practical difference: domestic § 120 priority for continuations has no hard time limit (as long as the application is copending with its parent), while foreign and provisional priority must be claimed within 12 months.
What happens if the priority claim is defective?
A defective priority claim — one that was not properly perfected or is invalid — means the application uses its actual filing date as the effective filing date, not the priority date. This can result in: prior art that arose between the priority date and the actual filing date becoming available against the claims; loss of ability to antedate prior art; potential invalidity of issued claims if the examiner or court determines the priority claim was invalid. Common priority claim defects: failing to include the priority claim in the application data sheet or specification; missing the 12-month deadline to file the non-provisional; the prior application not adequately disclosing the claimed subject matter (written description/enablement failure for the priority claim); and failing to list the correct serial number. Under AIA, the USPTO allows a petition to accept a priority claim filed after the 12-month deadline if the delay was unintentional — but this requires a petition, fee, and statement of unintentional delay.