How to Calculate a US Patent Expiration Date

Step 1: Identify the Patent Type

The rules differ by type:

• Utility and plant patents: Twenty years from the relevant filing date, as described below
• Design patents: Fifteen years from the date of grant for applications filed on or after May 13, 2015, and fourteen years from grant for earlier applications; no maintenance fees are due

The rest of this guide covers utility patents, which make up most portfolios.

Step 2: Find the Filing Date That Starts the Clock

Under 35 U.S.C. 154(a)(2), the patent term ends twenty years from the filing date of the application, or, if the application claims the benefit of an earlier US non-provisional or PCT application under 35 U.S.C. 120, 121, or 365(c), twenty years from the earliest such filing date.

Three dates do not start the clock:

• The filing date of a provisional application
• The filing date of a foreign application claimed under Paris Convention priority
• The date of national stage entry, for a US national stage of a PCT application; the international filing date controls instead

For a continuation, divisional, or continuation-in-part, the clock runs from the earliest non-provisional application in the chain, which is why every member of a patent family tends to expire around the same date.

Step 3: Check for Pre-1995 Rules

For applications filed before June 8, 1995, and patents in force on that date, the term is the greater of seventeen years from grant or twenty years from the earliest relevant filing date. Few such patents remain in force, but they still appear in older portfolios and in litigation over long-pending applications.

Step 4: Add Patent Term Adjustment

Patent term adjustment under 35 U.S.C. 154(b) compensates for USPTO delays during examination, such as failing to issue a first action within fourteen months or to issue the patent within three years of filing. The adjustment is reduced by applicant delay, such as taking extensions of time. The number of days is printed on the face of the patent, and it can be corrected by a request for reconsideration filed within the time allowed after grant.

Step 5: Add Patent Term Extension, If Any

Patent term extension under 35 U.S.C. 156 restores part of the term lost while a drug, biologic, medical device, or certain other products underwent regulatory review. It is limited to one patent per approved product, is capped at five years, and cannot leave more than fourteen years of term after approval. Extensions are granted on application after approval, so an expiration date calculated before approval may later change.

Step 6: Apply Any Terminal Disclaimer

A terminal disclaimer filed to overcome obviousness-type double patenting ties the patent's expiration to that of the reference patent. The disclaimed patent expires no later than the reference patent, and any patent term adjustment that would extend it beyond that date is lost. Always check the file history for a terminal disclaimer before relying on the adjusted date.

Step 7: Confirm Maintenance Fees Are Paid

A utility patent stays in force only if maintenance fees are paid. The fees are due at 3.5, 7.5, and 11.5 years after grant, can be paid without a surcharge during the six months before each due date, and can be paid with a surcharge during a six-month grace period afterward. If a fee is not paid by the end of the grace period, the patent expires at the fourth, eighth, or twelfth anniversary of grant.

A Worked Example

Consider a patent with the following history:

1. A US provisional filed on 15 March 2017
2. A US non-provisional claiming the provisional, filed on 15 March 2018
3. A patent granted on 4 June 2024 with 212 days of patent term adjustment and no terminal disclaimer

The provisional date is ignored, so the base term ends on 15 March 2038, twenty years from the non-provisional filing date. Adding 212 days of adjustment gives an expiration date of 13 October 2038.

The first maintenance fee can be paid without surcharge between 4 June 2027 and 4 December 2027, and with a surcharge until 4 June 2028. If it is not paid, the patent expires on 4 June 2028, more than ten years earlier than the calculated date.

If the same patent had a terminal disclaimer over a parent expiring on 15 March 2038, the adjustment would be cut off and the patent would expire on 15 March 2038.

Keeping Expiration Dates Accurate

Expiration dates drive pruning, licensing, and freedom-to-operate decisions, yet they are easy to get wrong: a missed terminal disclaimer, a PTA correction, or a lapsed fee can each change the answer. Portfolios are safest when the calculation is recorded with its inputs, so anyone can see which filing date, adjustment, and disclaimer produced the date. ArcPrime's portfolio management view calculates each asset's expiration from its prosecution record and flags terminal disclaimers and fee status alongside it.