What is the test for a plaintiff to prove that they have lost income due to negligence?

That said, the plaintiff must do more than provide particulars of the claim; he or she must also prove the loss on a balance of probabilities (see Scott v. Renton, para. 30). More often than not, income earned prior to the wrongful act constitutes the basis of choice for assessing past loss of earning capacity. On occasion, however, prior earnings are a poor indicator of actual loss.