It just doesn't work like that. Just out of curiosity, did you PAY this developer to work with you?
Think of it this way:
1) Imagine you are sitting alone in a room, with your fabulous idea and a great plan. Now fast forward through a year of sitting alone in that room. Are you any closer to having a business, or do you still just have that idea?
2) Imagine you and your developer together in the room. Fast forward a year and you may just have a business put together.
In other words, your idea has very little value on it's own. An idea is pretty useless unless it's in some form that can be executed, such as:
a. If you have an idea AND a lot of money, you can own the whole idea and pay to get it executed.
b. If you have an idea AND you know how to write a business plan (a real one) and get investors, you can sell off large parts of the business (usually more than half if its big) and get it executed.
c. If you have an idea AND you have a developer who believes in your idea and is willing to work for FREE, you can give that developer a big share of the business to execute it with you.
d. If your idea is SO GREAT that developers are beating down your door to help out for free, in return for a small share of the company, then go for it!
I guess the bottom line is, your idea has very little value unless there is some manner of execution. Just because you thought of it doesn't magically make it happen. If you have money to pay a developer, then go for it. If you want a developer to work on spec, you should compensate them.
I'm necessarily saying you need to do a 50/50 deal, but don't undervalue a contributor.
So, you claim to have done all that planning. Is that planning on paper, in a formal document format? Why are you offering the developer any equity at all instead of just paying him? Or, why is he working for 'free' right now?