How campaign budgets are usually built
Launch library · evergreen read

A campaign budget typically starts from the activities the strategy requires, costing out each one, before checking that total against realistically available funding, rather than starting from an available amount and simply trying to fit activities within it. Starting from strategy rather than from the available amount keeps priorities honest from the very first draft.
Building a budget this way keeps spending tied to strategic priorities, making it easier to see where cuts would actually cost the campaign strategically if funding falls short, rather than cutting whatever happens to be easiest to remove. That clarity becomes especially valuable during a difficult, resource constrained stretch of the campaign.
Because campaigns rarely unfold exactly as planned, a realistic budget also includes some contingency for unexpected costs or opportunities, since a budget with no flexibility at all can leave a campaign unable to respond when circumstances genuinely change. Even a modest reserve can make the difference between adapting well and simply stalling.