A patent may be enforced starting on the date it is issued by the USPTO (its "Issue Date"), and running for the length of its term, unless it expires earlier. After the patent expires, the invention is available to all.
To determine if a patent is still in force, you will need access to the USPTO's website. You can find most of the information in the text-based display, but not all. You will need to look at the patent image, which is in PDF format. You can also look the patent up in the European Patent Office's espacenet system or in Google Patents and retrieve the same text and PDF image. Use whichever system you find to be the easiest for you.
Note: The USPTO has come up with a Patent Term Estimator spreadsheet. The program allows you to estimate patent term by filling in information in a Microsoft Excel spreadsheet - see the USPTO website for instructions and a copy of the spreadsheet.
To determine if a patent is still in force yourself, follow these steps:
If the patent is an original-issue Utility Patent (not a Design Patent (number starts with "D" or "Des") or a Plant Patent (number starts with "P" or "Plt") or a Reissue of a Utility Patent (number starts with Re)) and the patent number is 4,999,999 or less - stop here. All such patents expired on or before August 31, 2010. If this shortcut doesn't apply, you will have to work through the procedure below.
Call up the patent on the USPTO patent database, the European Patent Office's espacenet system or in Google Patents, if you do not already have a printed copy. If you need help reading the patent, see our "How to read the first page of a patent" page.
Utility Patents and Plant Patents based on applications filed after June 8, 1995, (actual filing date, not priority date), have a term of 20 years from the US filing date* of the earliest non-provisional application** in the chain of parentage upon which the patent is based. For more details on how this calculation works, see our page on "Patent Timeline".
Utility Patents and Plant Patents based on applications which were pending on June 8, 1995 (actual filing date, not priority date), and any Utility or Plant Patent which was issued on or after June 7, 1978 and had not expired before June 8, 1995, have a term measured by the longer of 17 years from the date of issue or 20 years from the date of US filing* of the earliest non-provisional** application in its chain of parentage.
*= By "US filing date" we mean, if the US application claims priority from an earlier-filed foreign application (that is, it gets the benefit of a filing date in a foreign patent office for purposes of determining what is "prior art"), it is the actual filing date of the first application in the USPTO which starts the 20-year term, not the filing date of the foreign application.
NOTE: If the patent is based on a PCT application, the "US filing date" for the PCT application is its International Filing Date (listed on the patent as item  "PCT Filed"), not the date it entered National Stage (item  "371 Date").
**=By "non-provisional" we mean, well, not provisional. In other words, if the patent claims the benefit of the filing date of a provisional application, that provisional filing date does not start the term running***. You look at the actual filing date of the utility patent application to determine patent term. However , if the patent was a continuation, continuation-in-part or divisional of an earlier "regular" patent application, it is the filing date of the first filed earlier "regular" patent application which is used to compute patent term.
***=Additional note (thanks to Stephen Nipper for pointing this out) - in the unlikely event that the applicant chose to convert the provisional application into a "regular" application under 37 CFR 1.53(c)(3), instead of following the usual procedure and filing a new utility application claiming the benefit of the provisional, the provisional filing date DOES start the term. This is one reason why one should NEVER use that procedure - and the USPTO regulation establishing it specifically says so. Nonetheless, there might be some patents out there which are based on converted provisionals, and if so, their term is up to a year shorter than it might otherwise appear.
Utility and Plant Patents issued before June 7, 1978, had a 17-year term, measured from the date of issue, and have all expired.
Design Patents granted on applications filed before May 13, 2015, have a term of 14 years, measured from the date of issue.
Design patents granted on applications filed on or after May 13, 2015, have a term of 15 years, measured from the date of issue.
Note that some websites reported the change for design patents to a 15 year term as being effective on December 18, 2013. That is an error based on a misinterpretation of the original Federal Register announcement. The change was effective on the later of December 18, 2013, or three months after the US deposited a paper at WIPO relating to the Hague Convention. The deposit did not happen until February 13, 2015, so the change occurred three months after that.
Some patents have less than the usual life span because their terms are limited to the terms of earlier-issued patents. This is called a "terminal disclaimer", and is a result of filing two applications which claimed essentially the same invention. Terminal disclaimers will be marked on the later-issued patent. Sometimes these are flagged by an asterisk after the patent issue date, but sometimes they only appear in the text of the patent or with the "related application" data on the face of the patent. In rare instances, there will just be a note printed on the patent which says, "This patent is subject to a terminal disclaimer", but there is nothing on the printed patent indicating which earlier patent the term is linked to.
In most cases, you will need to go to the USPTO Public PAIR system and try to find the terminal disclaimer itself in the Image File Wrapper, if there is one. If the patent is too old to have an Image File Wrapper, you can look on the "Continuity" tab in PAIR or at the list of related applications on the patent itself - if there's only one prior patent in the chain, the terminal disclaimer nearly always refers to that patent. Call up that patent, and go through this whole procedure for it, and you will find out the common expiration date for both patents.
Once you know what patent the terminal disclaimer was based on, you need to consider what the terminal disclaimer said was the point at which the term was disclaimed?
Normally, for patents filed after June 1995 which have a 20-year-from-filing term, and where the patent with the disclaimer is a "child" of the base patent - for example, if it is a continuation, continuation in part or divisional of the earlier patent (this will nearly always be the case) - a terminal disclaimer will have little practical effect. The two patents would have had the same basic expiration date, anyway.
Note that a terminal disclaimer ties the term of a later-issued patent to the normal term of the earlier-issued patent. An earlier-than-normal expiration of the first patent, for example because the owner failed to pay the maintenance fees, does not affect the term of the patent subject to the disclaimer. This was affirmed in a 2011 district court case, Hoffman-La Roche Inc. v. Orchid Chems. & Pharms. Ltd. (D-NJ 2011), and by the Federal Circuit in the Pharmacia v. Par Pharmaceutical case (CAFC 2005)
Patents based on applications filed on or after May 29, 2000 (actual filing date, not priority date), might have had their terms extended for Patent Office delays beyond certain limits. Such extensions, called "patent term adjustments", are automatically given when the patent is issued, and they are usually marked on the face of the patent, flagged with "(*)". For example, see patent 7,613,700 - "(*) Subject to any disclaimer, the term of this patent is extended or adjusted under 35 USC 154(b) by 291 days." These adjustments are calculated mathematically based on a formula which takes into account when each office action was sent by the USPTO as compared with a standard for such actions, and subtracts any delays caused by the applicant's delay, and so on.
Special rule for patents issued between August 2009 and March 2010: The January 2010 Wyeth decision held that the USPTO had been calculating these adjustments incorrectly in some cases. Based on this decision, the USPTO announced in January 2010 that patents issued before March 2, 2010, which were pending for more than three years could have their adjustments recalculated if the patentee filed an SB131 form within 180 days of the issue date of the patent - effectively, then, this meant that extensions were available for patents issued after August 2009 and before March 2, 2010, and the last date anyone could file for a Wyeth adjustment would have been September 2, 2010. Not everyone who was eligible for extension applied for it. For those who did apply, and if the USPTO recalculated and discovered an error had been made, the patent term adjustment printed on the face of the patent would not be correct. However, any affected patent should be new enough to have the Wyeth request form available in the USPTO's Public PAIR system.
Special Cases: Some patents have had their terms extended based on extreme delays in government approvals outside the Patent Office. This is very unusual, and applies almost always to pharmaceuticals (for example, Claritin® or Prozac®), food products (Aspartame) or medical devices or procedures, where FDA approval can sometimes eat up most of the patent term before the product can be brought to market. It is also theoretically possible that a patent could have its term extended by Congress by the passage of a Private Law applying only to that patent - we say "theoretically" because this has not happened since the late 1980's, no current patents are subject to such extension, and the procedure was essentially rendered obsolete by the passage of 35 USC sections 155 and 156, which provide for the extensions noted above.
For a list of patents extended under sections 155 or 156 or by private law, see the Patent and Trademark Office's Extended Term List
Effect of Terminal Disclaimers (see section 2 above) on term extensions:
Extensions for FDA approval - term is extended past disclaimer date: In the Merck v. HI-TECH case, decided in March 2007, the Court of Appeals for the Federal Circuit held that if a patent is subject to a terminal disclaimer, the term extensions for regulatory review granted by section 156 of the Patent Law (35 USC 156) are added on after the terminal disclaimer date. It can safely be assumed that extensions under section 155 would be treated similarly.
Extensions for USPTO delays - term is not extended past the disclaimer date: Term extensions due to USPTO delay are governed by section 154 (35 USC 154(b)). Section 154(b)(B) says:
(B) Disclaimed term.— No patent the term of which has been disclaimed beyond a specified date may be adjusted under this section beyond the expiration date specified in the disclaimer.
While this section refers to "a specified date", as noted above most terminal disclaimers just disclaim term past "the full statutory term" of the other patent. There have been a few cases on this, and they have held that this reference to a "full statutory term" date would be a "specified date" under this section. Therefore, it can probably be considered as a general rule that term adjustment for USPTO delay cannot extend the life of a patent past a disclaimer date, whether that date is given explicitly or just by reference to the term of the earlier patent.
This would be noted on a certificate attached to the patent image on the USPTO database, usually as the last page in the image file.
On rare occasions, issued patents are withdrawn from issue on the order of the Commissioner of Patents. In these cases, the patents are usually not available on the USPTO database (but sometimes they are on other databases, such as the EPO's Espacenet, Google Patents or the for-pay systems).
Utility Patents: There are maintenance fees due at 3.5 years, 7.5 years and 11.5 years from the date of issue. The "payment window" opens six months before the due date (that is, 3, 7 or 11 years after issue - earlier payments are not accepted), and closes one year later (that is, 4, 8 or 12 years after issue). If the fee is paid during the "grace period" of six months after the due date ("Surcharge Date"), a surcharge is added. If the maintenance fees are not paid before the window closes, the patent expires as of the end of the grace period.
Note: Patents based on applications filed before December, 1980 (actual filing date, not priority date), were not subject to the payment of maintenance fees. Most of these patents have long since expired at the ends of their terms, so this exception will seldom arise.
You can use the USPTO's Patent Application Information Retrieval (PAIR) system to determine if maintenance fees have been paid. Enter the patent number on the first screen (you will need to use the pull-down menu to change "Application Number" to "Patent Number", or enter the application number, if you know it). On the next screen, click on the "fees" tab. Click on "Maintenance Fees - Retrieve Fees to Pay", and you will see a screen like this:
Look at the "Window Opens" and "Window Closes" lines. In this example, the seven and a half year maintenance fee is due between February 24, 2005, and February 24, 2006 (with a surcharge due if the fee is paid after August 25, 2005). Since both these dates are in the future (as this is being written in the fall of 2004), the patent is still current (also note the line at the bottom of the screen which says, "Currently there are no fees due."). If the maintenance fee is not paid before the "Window Close" date, the patent will expire as of the "Surcharge Date".
As it happened, the maintenance fees on this example patent were not paid, and the patent expired in August, 2005. If you look the patent up today, instead of the payment window display the PAIR system will give an error message saying "*ERROR: There is no statement available for the selected payment year because the Patent has expired."
You can also click on the "Maintenance Statement" selections to confirm that a fee was paid, and how much it was.
In December, 2004, the PAIR system was enhanced to note a status of "Patent Expired Due to Non-Payment of Maintenance Fees Under 37 CFR 1.362" for patents which have expired for that reason. It appears that this only affects patents which expired after the date the enhancement went into effect. Obviously, if the status has this note, then the patent is expired. If it does not, you still need to follow the process above to check if maintenance fees were, in fact, paid.
But be careful - even if it's expired because of non-payment of maintenance fees, the patent might still be revived: Patents which expired due to nonpayment may be revived, so long as the delay in paying the fee was unintentional.
Until December 2013, an application to revive a patent based on unintentional delay had to have be filed within two years of the end of the grace period, and this page used to say that if it had been two years since the patent expired it could be safely considered to be permanently dead. However, the Patent Law Treaty amendments which were instituted in December 2013 eliminated the two-year requirement, and patents can now be revived after that time just by paying the missing fee and a petition fee and stating that the delay was unintentional. The USPTO can request additional information, and they can reject such petitions, but it is unclear if they will do so. Therefore, at the present time, there is a finite risk that a patent which expired for non-payment of a maintenance fee may come back.
Just to be completely clear, the last paragraph only applies to expiration due to nonpayment of maintenance fees - patents which expired at the end of their term cannot be revived.
Plant or Design Patents: No maintenance fees are due on Plant or Design patents.
If a patent is declared invalid by a court, it becomes unenforceable. Unfortunately, there's no certain or easy way to know this.
If you have access to the Lexis or Westlaw or BNA USPQ databases (all available only for fees, unfortunately), you can try looking up the patent number in their databases of reported court cases to see if the patent might have been mentioned in a case report. Once you have a case citation you can look up the case in the Public Access to Court Electronic Records (PACER) system. You could also try just doing a Google search on the patent number and see if a reported case turns up, you never know.
If you are concerned about a patent, it may be advisable to have a patent attorney (for example, one of the attorneys at Brown and Michaels) do a validity study and opinion on the patent. The attorney will do a search to find prior art which might invalidate the patent, and will review the patent's file at the USPTO to see if there is anything which might affect the validity or scope of the patent. Feel free to contact Brown and Michaels if you think you might need this service.
Don't forget our "Patent FAQ" page - it has lots of information about patents and the patent process.
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