One last factor to think about is whether you need some kind of a safety net of benefits — the kind that regular employment often provides. If, for example, you have three kids who'll need braces over the next five years, take a look at how much a company dental plan will pay toward that expense and how much it's going to cost to replace it with a self-employment plan or no plan at all. The same goes if a member of your family needs extensive health care coverage. Sometimes, going it alone doesn't make financial sense.

Similarly, are you just a few years from retiring with a pension? Assess how much it's going to cost you to leave now (your company's human resources office can help you with this). It might be worth continuing your paid employment for a couple of years until retirement, so that you qualify for that pension — which will then make it financially easier to start your business.