How to use the treaty priority claim period calculator
Filing in one country first and abroad later only works if the later application is filed inside the priority period. The United States applies the same Paris Convention periods as Korea and the rest of the treaty countries, so this tool works in both directions: a foreign first filing followed by a US application, or a US filing followed by foreign ones.
The period is counted with the filing day excluded (Paris Convention Art. 4C(2)), which is why a 12 month period ends on the anniversary of the first filing rather than a day earlier. The start date, days left and days elapsed shown above all use that same rule.
Authority: 12 months for utility patents under 35 U.S.C. 119(a) and for a nonprovisional claiming a provisional under 119(e); 6 months for design patents under 35 U.S.C. 172 and for trademarks under 15 U.S.C. 1126(d); Paris Convention Art. 4C. Weekend and holiday filings are governed by 35 U.S.C. 21(b). Stated as of September 2026.
This calculator is for reference only and is not legal advice. Confirm dates with a registered patent attorney or agent before relying on them.
Frequently asked questions
The USPTO allows a delayed priority claim in limited circumstances where the delay was unintentional and the required petition, fee and statement are filed, and other offices have their own restoration rules. The requirements differ by office, so ask your attorney as soon as you notice the date has passed.
No. A provisional sets the priority date and the nonprovisional must follow within 12 months, but the Paris Convention period for foreign filings runs from that same earliest filing date, so both clocks start together rather than one after the other.