I think that it is important to draft a budget containing fixed expenses first.
In order to calculate a budget you would have to look at the regular expenditures that you have month to month. For example, a mortgage payment, a car payment, a student loan payment, or a tuition to your children’s private school are all considered fixed expenses because the payments remain the same over time.
In a business, the lease is a fixed overhead cost along with signed contracts from other service providers.
Most businesses need a combination of a fixed budget and a flexible budget. A flexible budget allows for mishaps or problems that arise in the industry that were unforeseen.
For example, the addition of competitors and a slower economy might cause a company to increase its advertising expense in order to yield more customers.