There are many different methods used to determine the media budget. Some of these are:

goal$-$driven $-$ based an estimate of the resources required to achieve the company's strategic goal.

percentage$-$of$-$sales $-$ this approach implies setting the budget as a fraction of the company's sales revenues

competitive$-$parity $-$ this approach implies setting the budget at par with that of a key competitor

legacy$-$ budgeting based on prior year expenditures

affordability $-$ setting the budget based on resources available for promotional activities

all the above methods