Patent expiry came 20.0 to 23.1 years after the priority date in 12 famous patents

I pulled 12 well-known patents from Google Patents on 2026-10-24 and compared each priority date with the expiry date Google shows. The usual rule is "20 years from filing", and it holds for five of them. The other seven ran from 20.84 to 23.08 years, or exactly 21.00 in three cases.

These are 12 patents I picked because they are famous, not a sample. Read the table as a set of examples, not as statistics.

The expiry date has two labels

On a Google Patents page, the event list near the top ends with a date labelled either Anticipated expiration or Adjusted expiration. I opened three of the twelve to check them. RSA and the cat patent say "Anticipated expiration". Apple's slide-to-unlock says "Adjusted expiration", and its date is 2028-01-24. Twenty years from its priority date, 2005-12-23, would be 2025-12-23, so about two extra years were added. "Adjusted" suggests the US patent office's term adjustment for delays during examination. Google's page does not state the cause, so that part is my reading.

Why 20.0 is not the only answer

• Old patents ran from the grant date. RSA was granted 1983-09-20 and expired exactly 17 years later, 2000-09-20. Cohen-Boyer was granted 1980-12-02 and expired 1997-12-02, also exactly 17 years later. For applications filed before 8 June 1995, the US term is the longer of 20 years from filing or 17 years from grant (USPTO MPEP 2701). Both were filed in the 1970s, so the 17 years from grant won.
• The priority date is not always the filing date. PageRank, the antenna and CRISPR each show a priority date about a year before the filing date Google lists, and the expiry is exactly 20 years after the filing date: PageRank filed 1998-01-09, expires 2018-01-09; the antenna filed 1997-10-02, expires 2017-10-02; CRISPR filed 2013-10-15, expires 2033-10-15. An earlier priority date with a later filing date is what you would expect from a provisional application, though Google's page does not say that. The touch-screen patent is a variation: it was filed 2008-04-11, but it expires 2027-09-05, about 20 years after September 2007. I did not look up the earlier application it builds on.
• Term adjustment can add time. That is the slide-to-unlock case above.

The status column has three values

• Expired - Lifetime (six): the patent ran its full term. 1-Click, RSA, PageRank, LZW, Cohen-Boyer and the antenna.
• Expired - Fee Related (three): the owner stopped paying maintenance fees. The cat patent, the tristate circuit and the anti-gravity shoes.
• Active (three): slide to unlock, touch-screen heuristics and CRISPR.

For the fee-related ones, the date Google shows is still the full 20 years (the cat patent shows 2013-11-02), and the actual lapse happened earlier. So the expiry date is when the patent would have run out, not when it stopped being enforceable. If you need the lapse date, read the legal events list.

Checking a whole list

By hand this is one page per patent. For a list, the steps are: normalise the numbers (uppercase, remove spaces and commas), fetch status, priority date, grant date and expiry for each, then compute the term and the time left. The last step is a few lines of Python once you have the records as JSON:

import json from datetime import date today = date(2026, 10, 24) # use date.today() for live data  for p in json.load(open("dataset.json")): expiry = date.fromisoformat(p["expirationDate"]) term = (expiry - date.fromisoformat(p["priorityDate"])).days / 365.25 left = (expiry - today).days / 365.25 print(f'{p["publicationNumber"]:<12} {p["legalStatus"]:<22} term {term:5.2f} y left {left:6.2f} y') 

Output on my 2026-10-24 data:

US5960411A Expired - Lifetime term 20.00 y left -9.11 y US7657849B2 Active term 22.09 y left 1.25 y US7479949B2 Active term 21.00 y left 0.87 y US8697359B1 Active term 20.84 y left 6.98 y US4405829A Expired - Lifetime term 22.77 y left -26.09 y US6285999B1 Expired - Lifetime term 21.00 y left -8.79 y US4558302A Expired - Lifetime term 20.00 y left -23.35 y US4237224A Expired - Lifetime term 23.08 y left -28.89 y US5443036A Expired - Fee Related term 20.00 y left -12.97 y US5136185A Expired - Fee Related term 20.00 y left -15.09 y US5255452A Expired - Fee Related term 20.00 y left -14.32 y US6025810A Expired - Lifetime term 21.00 y left -9.06 y 

A negative "left" means it had already expired. The three active patents had 0.87, 1.25 and 6.98 years left on that date.

Caveats

• Google's status is not a legal conclusion. The tooltip next to it says the status "is an assumption" and that Google "has not performed a legal analysis" and makes no representation about its accuracy. The priority date carries the same note.
• ISO dates (2027-09-05) compare correctly as strings. Other formats do not, so check the format before you compare.
• A term computed from the priority date is a rough estimate. Use the expiry Google shows for decisions.
• This is 12 patents, one run, one day. I did not check why each value differs.

Getting the records without opening each page

Disclosure: I built a tool for this. Google Patents Scraper on Apify takes a list of patent numbers or Google Patents URLs and returns legalStatus, expirationDate, priorityDate, filingDate and grantDate for each, with an option to include the legal events list. It looks patents up by number and does not search. The price is $0.003 per patent on the free and Bronze plans (a little less on higher plans) at the time of writing, and numbers that are not found are not charged.

An AI assistant helped me draft this article. I checked the numbers against the raw data and opened three of the patents on Google Patents myself on 2026-10-31. The data was collected on 2026-10-24.