The first thing you need to know when creating a budget is that it is wrong from the start.
In the world of accounting and finance, we like things to be precise and tie out neatly. A budget, on the other hand, is meant to be a predictive tool and a roadmap to help you get to where you are going.
When you enter an address into your GPS, you often get three to four different routes you can take to get to your destination. Sometimes the route has construction or other traffic impediments along the way. Think of a budget somewhat the same way. You build assumptions that you can change based on the route you decide to take and the detours you may face along the way.