[argonaut]

Some points:

1) The new co-founder does not deserve 50%. There are only two instances in which I might see him getting 50%: he either brings in money (invested into the company), or he takes a significantly smaller salary than you take. What you give him will depend on how you perceive his value, and how much you need him at this point. Something like 30% is a reasonable starting point.

2) Going off point #1. Are you sure you need a new technical co-founder? Do you feel like this is a gap in your knowledge? Because you may very well be able to forgo the technical co-founder route, and simply start hiring 1 or 2 technical employees. You would need to pay these employees salaries. You would pay them slightly below-market salaries and equity in the range of 1-3%. Nonetheless, there are very compelling benefits to having a co-founder with very strong technical skills.

3) What concerns me the most is that its unclear how well you know this potential new co-founder. What did you think of his part-time work? Was it amazing? Even if his part-time work was amazing, it is still unclear if he is the right co-founder for you. Did he work remotely? How well do you guys get along? How well do you guys communicate? If he worked remotely, it will be much harder to assess how you get along with him.

Something I've noticed about YC, for example, is that I keep running into founding teams (of YC companies) that consist of founders who knew each other as 1) friends from high school, 2) friends from college, or 3) worked together at the same company for 1 or more years. I suspect that YC would be willing to hire 2 co-founders of slightly-above-average intelligence who are best friends from college over 2 brilliant co-founders who worked on one class project together. One of the reasons is because the #1 reason (or at least one of the biggest reasons) for a funded startup failing is co-founder disputes.