I’ve always been wondering how a reasonable deadline could be decided on. If you do risk management, you must know that the best we can do is to put our estimate about risk versus schedule. But most customers don’t buy that. If you’ve ever tried to put a risk estimate on their table, they will no doubt choose the one with earliest deadline (yeah, and the most risky one).

Nevertheless, if you want to give the customer a firm deadline and still want to be reasonably flexible, Bert Webb gives a formula. Basically the formula just gives more weight to the realistic deadline but still gives you some buffer (in the face of the most pessimistic one). In my opinion, how you pick the weight depends on the team you have.

Estimating Realistic Project Deadlines