Elliot R. Schiff Legal Malpractice Law Blog on Lawyers.com

While recovery in a legal malpractice lawsuit for the sum of the judgment entered against the client without proof of payment appears to suffice, the same is not true where the client is denied full or complete compensation.  That is, the client must not merely demonstrate what the result should have been, but also must establish the amount of money that would have been collected. 

Awarding damages above that which the plaintiff could have actually collected in the underlying suit would result in a “windfall” to the plaintiff.  Recovery then is limited only to the extent of the solvency of the underlying person against whom the judgment would have been entered but for the attorney’s negligence.  In other words, if the plaintiff could not have collected a full judgment from the defendant in the underlying case, the attorney’s negligence did not injure the client in that amount or to say it otherwise, one cannot lose what one never could have had. 

This ensures that the plaintiff is in no better position by bringing suit against the attorney than if the underlying action had been successfully prosecuted.  Solvency is measured at the time that the judgment should have been secured.