[DirtyAndy]

How much can you expect to earn from a startup? Zero. Most startups fail, or are just not viable as businesses. There is no "build it and they will come". Even if it worked ramping up to post tax post living costs personal profit of US$40K in one year would be difficult. Obviously thousands of people achieve it every year, but that is out of millions that try and get something started.

Also, if in one year you built a business that achieved that, you'd have to imagine it would continue to grow and make exponential amounts of money, so lets say year 2 you make $200K - why would you want to go to grad school then!?

Unless you've developed a minimum viable product and proven that people are willing to pay, if you really want to go to grad school, this would have to be the worst way about it. Get a normal job, a loan or whatever else. If it takes longer to get there then it takes longer.