This brief note is not legal advice and is for educational purposes only.
This area can get complicated and you really should contact your attorney.
PCT stands for Patent Cooperation Treaty. It is an agreement between countries that allows for the reservation of patent filing rights. Put very simply it acts like an umbrella in reserving rights for an inventor to file in a foreign country or region at a later date.
Typical US usage
You only filed a US utility application (aka non-provisional patent application)
This is a typical case for a US filed patent application. Assume that you filed your patent application on MM/DD/YYYY. If you want to reserve rights to file in foreign countries you MUST file a PCT application within 1 year (MM/DD/YYYY+1) AND claim priority to your US patent application. (Yes, leap year issues, etc. – just file it a day early.)
You filed a US provisional application and want to file a US utility application AND a PCT application
If the US utility application is to claim priority to the provisional it must be filed within one year of the provisional application’s filing date. The same rule applies to the PCT application. The best practice regarding priority is to file the US utility application at least a day before filing the PCT application. Then file the PCT application and in the PCT application claim priority to BOTH the provisional date AND the utility date. This way, if for some reason an issue arises, you’ll have at least one priority date. A note on dates – make sure the utility and PCT have at least 1 day difference in filing. For example, if the 1 year ends on YYYY-02-13 you can file the US utility application on YYYY-02-12 and the PCT application on YYYY-02-13. There MUST be at least one day difference otherwise you’ll not get the priority date.
You filed a US provisional application and ONLY want to file a PCT application.
Yes, this can be done and later you can enter into the US via either a 371 (35 U.S.C. 371) or via a 111(a) (35 U.S.C. 111(a)) route. There are several serious considerations on which route you use. You really need to talk to an attorney on taking this route.
The time delay to file a national or region application is generally 30 months from earliest claimed priority date. Some countries vary (Canada is 42 months with payment of a fee).
Here’s a link to the time limits: https://www.wipo.int/pct/en/texts/time_limits.html
Discuss with your attorney BEFORE filing. Verbum sap