At the rate we talk about dates in patent law, you’d think we would be drying them out and shipping them to super-fruit-eating customers.

Dad jokes aside, there are five critical dates in the life of a patent. In chronological order, here are their names:

1. priority date;
2. filing date;
3. publication date;
4. issue date; and
5. expiration date.

These dates are key to understanding both patentability—novelty and non-obviousness—and enforceability. These dates do depend on and build on each other. We’ll flip the priority date and the filing date around so that they make more sense.

1. Filing Date

The filing date is fairly straightforward. This is the date that a patent application was filed with the patent office. This is when the process of getting a patent starts. While it’s easy to know, since you were the one who made the filing, make sure to check your official filing receipt to ensure the expected date is shown as your filing date.

International Filing Date

When you use a Patent Cooperation Treaty (PCT) application, be mindful that the filing date is not the date that you enter the U.S. national stage, but rather the date the PCT application was filed. This is called the international filing date. For purposes of your U.S. national stage application, you should consider the filing date to be the international filing date. The day you file the national stage application is called the “§371 Date,” which is primarily an administrative date.

It helps to think about a PCT application as being filed with respect to the United States at the time the PCT application is filed, and then extended to the United States when you begin the national stage.

2. Priority Date

To get a patent, it has to be novel and not obvious in view of the prior art. I’ve written plenty on what constitutes prior art—check that out here. Suffice to say, we need a cutoff date to decide what prior art can be used by the patent office in an office action to try to reject your patent application. The priority date is the cutoff date.

Additionally, the grace period for prior art originated by you is calculated from the priority date. This means that any public disclosures or offers for sale, originating from you, that are made later than 12 months before the priority date are not prior art.

For a new, original application, the priority date defaults to the filing date. However, the priority date can be earlier than the current application’s actual filing date if you “claim priority” to another patent application. You can claim priority to a variety of other patent applications, such as:

• a provisional patent application,
• a foreign patent application,
• a PCT patent application, or
• a parent U.S. application (e.g., the new application is a continuation, continuation-in-part, or divisional application).

Accordingly, if there is a priority claim—sometimes called a “benefit” claim when dealing only with U.S. applications—your application’s priority date may be earlier than its filing date.

3. Publication Date

A patent application is normally published in the United States on a Thursday—yes that’s the rule—18 months from its priority date. I told you these build on each other. This publication is a representation of the application in whatever state it is in when the patent office begins preparations for publication. Usually, given how long it takes for examination, publications represent the as-filed state.

There is a huge tactical advantage to ensuring your publication is closer to the issued state, which I’ll get into below. Keep reading.

Design Patent Applications Aren’t Published

Design patent applications will not have a publication date, since they’re not published until and unless issued as a patent.

4. Issue Date

The issue date is possibly the most straightforward date of all five. In the United States, this is the Tuesday—yes, that’s the rule—that the patent application turns into a patent. It doesn’t depend on the other dates, and it’s usually 4–6 weeks after you Your invention changes from “patent pending” to “patented” on the issue date.

5. Expiration Date

The expiration date has to be calculated. Thankfully, now that the TRIPS / Uruguay Round Agreements Act transition is over, it is easier than it used to be. Terms are calculated differently for utility and design patents.

How to Find a Utility Patent Expiration Date

Here’s how you can calculate a U.S. utility patent’s expiration date:

• The date that is the earliest of:
  • the current application’s actual filing date,
  • the international filing date, if the current application is or continues from a PCT U.S. national stage application, or
  • the filing date of the earliest parent U.S. non-provisional patent application in the patent family, if the current application is a child application (e.g., a continuation, continuation-in-part, or a divisional application);
• Plus 20 years;
• Plus any time added via Patent Term Adjustment;
• Minus any time disclaimed via a Terminal Disclaimer.

How to Find a Design Patent Expiration Date

Design patent terms are even easier. Here’s how you can calculate a U.S. design patent’s expiration date:

• The issue date;
• Plus 15 years (if filed on or after May 13, 2015) or 14 years (if filed before May 13, 2015);
• Plus any time added via Patent Term Adjustment;
• Minus any time disclaimed via a Terminal Disclaimer.

There you have it—the five key dates for patents. These dates will come up throughout the process of applying for a patent, and they will drive a variety of deadlines and activities throughout the process.

Bonus: Calculating a Patent’s Term of Enforceability

A patent is enforceable during its term. Now that we have these dates down, it is really easy to know the enforceable term of a patent: from the issue date to the expiration date.

Final Thoughts

These are the dates that whoever is managing your IP portfolio should know for every patent application and patent it contains. They’re essential to know for enforcement, valuation, and maintenance. If you’re unsure of who is tracking these dates for you or what they are, just ask your IP attorney—they’ll know.