The best way to split equity in any bootstrapped company on the planet is called Slicing Pie. It is a formula for not only determining a perfect split, but also the right buyout price if someone leaves the company.
When you, your developer, or anyone else dedicates time or contributes money or ideas or anything else and does not get paid, they are essentially betting the fair market value of their time or contribution on the future outcome of the company.
Their equity should reflect their bets relative to everyone else's bet.
It's a simple, but powerful concept that is used all over the world.
Every other method for dividing up equity is basically a guess. Only Slicing Pie applies a logical formula that always gives you the right answer.
I've written a book on this subject and you may have a copy if you contact me at SlicingPie.com