When Does a Patent Expire? A Complete Guide to Patent Term

A US utility patent generally expires 20 years from its earliest effective US non-provisional filing date, as set out in 35 U.S.C. § 154(a)(2). However, the actual expiration date can shift earlier or later depending on three key factors: patent term adjustment (PTA), which adds days for USPTO prosecution delays; terminal disclaimers, which can cap the term to match a related patent; and maintenance fee payments, which must be made at 3.5, 7.5, and 11.5 years after grant to keep the patent in force. Design patents filed on or after May 13, 2015 last 15 years from grant and require no maintenance fees. This guide focuses on utility patents.

Scope: This article covers US utility patents under the current 20-year-from-filing regime (applications filed on or after June 8, 1995). Patents filed before that date may be governed by the 17-year-from-grant term. All dates and examples assume US law.

The 20-Year Base Term Rule

Under 35 U.S.C. § 154(a)(2), a utility patent's term begins on the date the patent is granted and ends 20 years from the date on which the earliest US non-provisional application in the patent's continuity chain was filed. This is the “earliest effective filing date” for patent term purposes.

The 20-year clock starts ticking from the filing date — not the grant date. That means a patent that spent 4 years in prosecution effectively only has 16 years of enforceable patent term remaining at the time of grant (before adjustments).

Earliest Effective Filing Date and Why It Matters

The earliest effective filing date is the filing date of the oldest US non-provisional application from which the patent claims priority under 35 U.S.C. § 120. For a standalone application with no parent cases, this is simply the application's own filing date. For continuations and divisionals, the date traces back through the entire chain to the original parent.

Provisional applications (filed under § 111(b)) do not affect the 20-year term calculation because § 154(a)(2) specifically excludes them. However, they do provide an earlier priority date for prior art purposes.

For a deeper dive, see our guide on how to find the earliest effective filing date for patent term.

Patent Term Adjustment (PTA)

35 U.S.C. § 154(b) provides patent term adjustment to compensate applicants for certain USPTO delays during prosecution. PTA is measured in days and is added to the patent's expiration date. The three categories of delay are:

1. A Delay: Failure by the USPTO to take certain actions within 14 months of filing, 4 months of a response, or 4 months of certain events.
2. B Delay: Failure to issue a patent within 3 years of the actual filing date, excluding applicant-caused delays and certain other periods.
3. C Delay: Delays caused by interference proceedings, secrecy orders, or successful appellate review.

The total PTA is calculated as A + B + C − overlap − applicant delay. A patent with 200 days of PTA will expire 200 days later than the base 20-year term.

For a detailed comparison with patent term extension, see our article on patent term adjustment vs patent term extension.

Terminal Disclaimers

A terminal disclaimer is a statement filed during prosecution (typically to overcome an obviousness-type double patenting rejection) in which the patent owner agrees to shorten the term of one patent so that it expires no later than a related patent. When a terminal disclaimer is in effect, the patent's expiration date is “capped” to match the referenced patent's expiration date — even if the uncapped term would be longer.

For more details on how terminal disclaimers affect expiration, see our dedicated guide on how terminal disclaimers affect patent expiration.

Patent Term Extension (PTE)

35 U.S.C. § 156 allows patent term extension for patents covering products subject to regulatory review by the FDA or USDA. PTE compensates the patent owner for time during which the patented invention could not be commercially marketed due to required regulatory approval.

PTE applies primarily to drugs, medical devices, food additives, and color additives. Because PTE requires a separate application to the USPTO, applies only to specific product approvals, and involves complex FDA timing calculations, our Patent Expiration Calculator currently computes PTA but does not include PTE. Learn more in our PTA vs PTE comparison.

Maintenance Fees and Their Role

Even after a patent is granted and its term is properly calculated, the patent owner must pay maintenance fees to keep the patent enforceable. Under 35 U.S.C. § 41, maintenance fees are due at:

• 3.5 years after grant
• 7.5 years after grant
• 11.5 years after grant

If a maintenance fee is not paid within its window (including a 6-month grace period with a surcharge), the patent expires prematurely. The USPTO Maintenance Fee lookup tool can show whether fees are current.

Worked Example: Calculating Expiration for US 9,982,190

Common Mistakes

• Confusing filing date with grant date. The 20-year term runs from the filing date, not the date the patent was issued.
• Ignoring the continuity chain. If a patent is a continuation of an earlier application, the 20-year clock started with the parent's filing date. See our guide on continuations and divisionals.
• Counting provisional filing dates. Provisional applications do not affect the 20-year term calculation.
• Forgetting maintenance fees. A patent with a perfect term calculation still expires early if maintenance fees lapse.
• Overlooking terminal disclaimers. A TD can silently cap a patent's term years before the 20-year mark.

Last reviewed: April 2026

Legal disclaimer: This article is for informational purposes only and does not constitute legal advice. Consult a registered patent attorney or agent for advice specific to your situation. patentreply.ai is not a law firm.