How to use the patent challenge window calculator
Korea handles patent invalidity through a trial at the Intellectual Property Trial and Appeal Board, and the timing question is mostly about who may file. The United States splits the same ground into separate proceedings before the Patent Trial and Appeal Board, and the timing question is about which door is open on a given date. Enter the grant date and, if you have been sued, the service date, and the calculator maps the windows.
How the dates are counted — every window on this page is measured in whole months or years from the grant or service date and lands on the matching calendar day, with the last day of the month used when that day does not exist. Deadlines shown rolled to the next business day follow the weekend rule in 37 C.F.R. 1.7. The same measuring rule is used for all four dates so they stay consistent with each other.
Legal basis — a post grant review petition must be filed not later than 9 months after the grant of the patent (35 U.S.C. 321(c)), and an inter partes review petition may not be filed until after that same 9-month point or the termination of a post grant review (35 U.S.C. 311(c)). A petitioner served with an infringement complaint is barred from inter partes review more than 1 year after service (35 U.S.C. 315(b)). Ex parte reexamination may be requested at any time during enforceability (35 U.S.C. 302). Figures are current as of September 2026.
This calculator is for reference only and is not legal advice. Consult a registered patent attorney about your specific situation.
Frequently asked questions
No. It reaches patents examined under the first-inventor-to-file rules introduced by the America Invents Act, so older patents generally fall outside it and inter partes review or reexamination is used instead.
The bar in 35 U.S.C. 315(b) is written for inter partes review. Reexamination has its own requirements and timing, so check with a patent attorney before relying on either route.