[67726e]

I think it's going to entirely depend on what type of app you have. Much like your parent comment, my experience with building an app was that very little code could actually be shared. In my case we had some fanciful design that would largely have to be custom code for each platform. Thinks like API calls, validation, business logic could be shared but that was negligible compared to the platform specific code.

[eightysixfour]

Yes, and that's always going to be the case with cross platform development. Fancy UI/UX is going to be highly platform dependent, while projects that have more model/controller code are going to be easily shared.