Ask HN: Co-Founder split

Hello.

I have been a fan of HN for a while and this is my first post.

I am the only founder of my startup and I have been working on it in my spare time (20-30h / week) since May. I work full time in an angel investor network.

I decided to invite a co-founder because:

1. It's has been very lonely so far. I need somebody to share ideas, brainstorm, cry/laugh together, cheer when things go wrong, etc.

2. I am lacking some skills that I need to run the company. For example, I do a little bit of programming but not enough.

3. My time is limited. I would like to keep working in the angel investor network as long as I can (it's fun and I am meeting interesting people), but I look forward to work full time in my startup.

I have been working for a couple of months with a freelance developer. He is young, smart and has more skills than programming. We work together well and I enjoy working with him.

He has told me he would like to join the startup. I want to invite him as a co-founder.

He is still in the university (finishing mid 2012) and he can work in the startup for 30h/week.

What I want to do is this: keep my current job and pay him enough to cover his expenses (25% of my salary) so I can have him for 30h/week. What I will pay him is half of his market (odesk) price. I will work 20h/week.

So I will give him a share of the company because I want him to be a co-founder, not an employee.

I got the idea and I have spent $5,000 for developing a demo, legal fees, trademark registration etc. I also have spent around 500 hours of work myself.

How much of the company should I give him* so he can feel he is a co-founder (not an employee) and taking into account I am the one taking most of the risks.

Thanks for your help. Sorry for the poor English.

*We will do a vesting of the shares, of course.