The OP hasn't asked the right questions, IMO. For most startups, the thing that causes success isn't just great hacking talent. Heck, a lot of startups really

The OP hasn't asked the right questions, IMO. For most startups, the thing that causes success isn't just great hacking talent. Heck, a lot of startups really aren't solving a software problem so much as they are solving a market problem. But even if it is a really hard coding problem that you need a star for... The big question is whether he's an entrepreneur or not. Questions to ask him (and yourself): 1. How much traction would it take for you to quit your day job? 2. Which evenings and weekend days are you willing to set aside for this project moving forward (at a minimum). 3. How many months can you go without a paycheck (related to #1)? 4. Do you like non-coding problems? UX? Copywriting? marketing? SEO? (i.e. are you willing to evolve as a founder? I have a long post about this here: http://www.tonywright.com/2008/startup-founder-evolution/ http://www.tonywright.com/2008/startup-founder-evolution/ ) In terms of parting with equity, the equation should come down to risk/value. If you're both committing to spending 10h per week on this, then he deserve a largely equal slice. If you're quitting your day job and going 40h per week (or have 300h already sunk into it), then you're risking more and deserve a bigger slice. Be careful about overvaluing what you've done so far. A startup is a multi-year commitment. A few months of weekend and evening time is a tiny percentage of value creation compared to what's been contributed at the end.