There are two common approaches for calculating pain and suffering in a personal injury lawsuit. We list these two methods below. Pain and Suffering Multiplier: This is the most common approach. Your Houston auto accident lawyer will add up your special damages, then multiply them by a certain number, usually between 1.5 and 5. This number is determined by a variety of factors, and your personal injury lawyer will understand how to calculate it. Pain and Suffering Per Diem: The goal while using this method is to ask for a set dollar amount for every day that you (the plaintiff) experienced pain and suffering after your accident.