A freedom-to-operate opinion may be done in combination with a “validity and enforceability” opinion. A validity and enforceability opinion is a legal opinion as to whether a given patent is valid and/or enforceable. In other words, a validity opinion is a legal opinion or letter in which a patent attorney analyzes an issued patent and provides an opinion on how a court might rule on its validity or enforceability.

Validity opinions are often sought before litigation related to a patent. The average cost of a validity opinion (according to one 2007 survey) is over $15,000, with an infringement analysis adding an additional $13,000.

The cost of these opinions for US patents can run from tens to hundreds of thousands of dollars (or more) depending upon the particular patent, the number of defenses and prior art references, the length of the prosecution file history, and the complexity of the technology in question.