If it is at all possible, you should start your business without any funding beyond what you have available. Do this by starting slowly and in conjunction with present employment. Start your business by working evenings and weekends while keeping your present job as long as practicable. This way, if the business does not meet your expectations, you have not incurred debt and will still have a job!
However, depending on the nature of the business outside funding may be necessary. For example, expensive equipment or initial stock may be required. When determining your financing needs, remember that nearly everyone underestimates what is required, so be careful and do your planning accordingly. And of course, don't forget to factor in contingency - sickness, bad weather, equipment breakdown, etc. Anything that increases the time line to profits! Best you figure on a year before you see a profit. Here are some items to keep in mind when preparing your startup budget: