# How do you calculate theoretical yield?

Reactant $\rightarrow$ Product
("moles of product")/("moles of reactant") xx 100% = Yield
Of course, you need a balanced chemical equation, and specific quantities of reactant. Often one reactant is present in excess, and the other reactant is the limiting reagent. Chemists would gladly accept yields of 80-90%. However, in multistep reactions, even such good yields would be much reduced after 4-5 steps, and at each step the chemist loses material.
Natural product chemists, who design syntheses and synthesize complex natural organic products, would typically start with $k g s$ of material. After 10 or more steps, they would be literally be working with milligram quantities. This is one of the reasons why natural products chemists make bad boyfriends and girlfriends, or even poor acquaintances. At the end of a multistep organic synthesis, they become quite mad and obsessive.