If you use an agile model you will develop the most important features first. What this does is every week keeps you focused on the top priority and ensures tha

If you use an agile model you will develop the most important features first. What this does is every week keeps you focused on the top priority and ensures that when the budget runs out, the most important features will be done. The reality is that if there are 100 units of work and only 80 units are possible based on the budget, either the client will be unhappy because you told him 100 units were possible or you will be unhappy because you did 100 units of work for 80 units worth of pay. It is much better to just do the highest priority 80 units first and then see if the last 20 units are really necessary. When they actually have a working product in front of them, often times clients will realize it isnt worth delaying to get the last few bits.