In Fera v. Village Plaza  396 Mich. 639, 242 N.W.2d 372 (Mich. 1976), the landlord signed a lease with Fera for a bookstore, and then breached.  Fera has damages from loss of business, but how to calculate such loss, since the business never opened?  The Court found that it is not necessary to show what the damages are "with certainty", but only that the plaintiff, "lay the basis for a reasonable estimate of the extent of the harm measured in money."  It is impossible to know how much money Fera would have made, but it is possible to get a good estimate based on profits from similar businesses and other economic data.