Damages for a valid, enforceable, and infringed patent are determined relative to outcomes in a but-for hypothetical "but-for" marketplace in which the alleged infringer chooses its best non-infringing alternative.
Damages can include the patent holder's lost profits -- including lost sales and price erosion, depending on the nature of the "but-for" marketplace -- but are no less than a reasonable royalty that emerges from a hypothetical negotiation between a willing licensee and licensor and informed by their respective non-infringing alternatives.
Experienced providing patent damages expert testimony and consulting on behalf of plaintiffs and defendants in many industries, including the following.