What percentage of time is saved and costed doing TDD.
I assume this percentage of cost and reward changes during a projects life-cycle.
I'd imagine the initial phase has a lot more cost but little rewards attached. Further on (during re-factoring) you get the benefit of your tests.
I've heard anywhere from 30-50% of your time is writing unit tests. However that doesn't take into account the time saved from writing those tests.
What's everyones' experience with this?
EDIT Whats the time saved as well as the time cost? In bug fixing and refactorablity?