The first thing you need to know is you total income after taxes. Calculate the total from all sources, such as primary job, second job, child support and anything else you receive money from on a regular basis. If you consistently get overtime you can use that too. This will be the figure you have to work with. If you are self employed the first thing you need to budget for is income taxes. You may have federal, state and social security taxes that you need to set aside. If you don’t know what tax bracket you’re in and how much you should put away, you should check with an accountant. You don’t want to figure your taxes for the year and find out you haven’t put enough away.