Patent term extension for drugs, and the formula behind it

The US Patent and Trademark Office's list of patents extended under 35 U.S.C. 156, updated through Sept. 8, 2026, has 1,141 entries. The median extension is 1,025 days, about two years and 10 months, by GxRadar's analysis of the USPTO's published spreadsheet¹. Some 171 patents received the five-year maximum. Another 116 got less than a year.

Each of those extensions pushed back the date a generic version could launch without a patent fight. Patent term restoration was the brand companies' share of the 1984 Hatch-Waxman bargain. In exchange for an abbreviated route to approval for generics, Congress gave innovators back part of the patent life lost while a drug was tested and reviewed.

This explainer covers the formula, the two caps that limit it, how FDA and the USPTO divide the work, and what the agencies' records show. GxRadar's overview of the Hatch-Waxman Act covers the generic side of the bargain.

Why the extension exists

A drug patent runs 20 years from the first filing of the application, a term that took effect for patents granted after June 8, 1995, under the Uruguay Round Agreements Act, according to FDA's questions and answers on the program⁴. Before that, patents typically lasted 17 years from issuance. Companies usually patent a compound long before it is sold, so years of testing and FDA review eat into that term.

Title II of the Drug Price Competition and Patent Term Restoration Act of 1984³, titled "Patent Extension," created the remedy "to compensate patent holders for marketing time lost while developing the product and awaiting government approval," FDA says. The same FAQ notes that FDA's regulations for the program are at 21 CFR part 60.

The formula in the statute

An extension equals the regulatory review period that falls after the patent was issued, adjusted three ways, under 35 U.S.C. 156(c)². FDA defines the two phases of that period in 21 CFR 60.22⁵: the testing phase runs from the date an investigational new drug exemption takes effect until the marketing application is submitted, and the approval phase runs from submission to approval.

Source: 35 U.S.C. 156². Patents issued before the 1984 law for products already in testing faced a two-year cap instead, and the USPTO list shows 124 extensions of exactly two years, all on patents originally set to expire between 1988 and 2002.

Other conditions apply. The patent must not have expired or been extended before, and the approval must be the product's "first permitted commercial marketing or use," the statute says². For drugs, FDA reads "product" as the active ingredient; a new salt or ester of a previously approved acid can qualify, but a new acid of a previously approved salt cannot, FDA's FAQ explains⁴. The application must reach the USPTO within 60 days of FDA approval.

A worked example

Figures below are hypothetical, chosen to show how the caps bite. In each case the patent issued before testing began, testing lasted six years and FDA review took one year, so the eligible period is three years plus one year, or four years.

FDA gives its own example: a product eligible for the full five years that "had ten years of original patent term left at the end of its regulatory review period" could count only four of the five, according to the FAQ⁴. A product with 14 or more years of patent life left after approval gets no extension at all.

Who does what at FDA and the USPTO

USPTO decides the length. "PTO is responsible for determining the period of patent extension. FDA defers to PTO on all matters involving the construction and validity of patent claims," FDA says⁴. FDA's job is to confirm eligibility and to determine the regulatory review period from its own records.

FDA publishes each determination in the Federal Register, listing the testing and approval phases and the dates used. Anyone then has 180 days to file a due diligence petition arguing that the applicant dragged its feet, and 60 days after a due diligence determination to request an informal hearing, under the procedures in 21 CFR part 60⁶. FDA's FAQ states that "at the present time no due diligence petition has been submitted to FDA."

GxRadar counted FDA's Federal Register notices titled "Determination of Regulatory Review Period for Purposes of Patent Extension," which cover drugs, biologics and medical devices.

Source: GxRadar count of Federal Register documents from FDA, retrieved Nov. 5, 2026. The patent office describes its own procedures in section 2750 of its Manual of Patent Examining Procedure⁷, including interim extensions that keep a patent alive while an application is pending.

What the USPTO records show

Two USPTO spreadsheets give a sense of scale. The list of applications filed in the past five years, updated through Sept. 8, 2026, has 714 applications covering 696 patents and 324 product names, by GxRadar's count¹. Companies sometimes apply for more than one patent on the same product, though only one can be extended for a given review period. Filings ran at 158 in 2023, 166 in 2024 and 150 in 2025.

Source: GxRadar analysis of the USPTO list of patent terms extended under 35 U.S.C. 156¹, updated through Sept. 8, 2026. Extensions stated in years were converted at 365.25 days. The list covers drugs, biologics, devices, food and color additives and animal drugs, and excludes patents that received only interim extensions. Of the 172 in the top row, 171 show the five-year maximum (stated as five years, or 1,825 or 1,826 days); one entry shows 2,494 days.

Where generics feel it

An extension changes the date in the Orange Book. Within 30 days of receiving a certificate of extension, the brand must file a corrected expiration date on Form FDA 3542, under 21 CFR 314.53⁸. A generic applicant that chose to wait for the patent, rather than challenge it under Paragraph IV, now waits for the new date, and FDA may grant tentative approval in the meantime.

Extensions also stack with other protections. Pediatric exclusivity adds six months to listed patents and exclusivities, and regulatory exclusivities such as new chemical entity exclusivity run separately from any patent, as described in GxRadar's guide to the Orange Book. The USPTO says it typically updates both lists quarterly; the current editions run through Sept. 8, 2026.