1. Get a lawyer. The advice they give you should outstrip anything you read here. 2. Prepare to cut your losses in a worst case scenario. The best time to cont

1. Get a lawyer. The advice they give you should outstrip anything you read here. 2. Prepare to cut your losses in a worst case scenario. The best time to contractually quantify ownership stake is before you enter into the engagement. By the end, you have neither contractual support for your expected ownership stake, nor the leverage to ink it into a legally binding document. 3. (my $0.02) Practically, the most you may get from this scenario is a very expensive learning experience. Whether or not you have the grounding to enter legal proceedings (or threaten that), the payoff compared to the mental and financial cost of litigating are likely not in your favor. Sorry this had to happen to you. It happened to me, too. I learned a valuable lesson when it comes to doing this kind of work -- you need to get an airtight legally binding document before you start working, or else you'll be exploited. That your business "partner" never formally entered into a contract with you likely indicates the latter.