(Actual yield/theoretical yield) x 100
it is never 100% yield
in the theoretical yield you assume no product is Iost + all reactants react fully
Atom economy how many atoms must be wasted in theory
Percentage Yield tells us the practical efficiency of the process and how much is lost by:-
the practical process of getting the product
as a result of reactions being incomplete
reaction can be reversible (can be improved by changing the conditions)