I want this much. When can I get it?
We create a fixed-scope plan in response to the question of “when will all of this be done?”
There are 3 steps here
Sum the product backlog items
Estimate velocity as a range
Use the sum of the backlog divided by the velocity range to determine a date range
What we know
The project size is 120 points
Velocity is in the interval 15-20 (check this to calculate the range with %90 level of confidence)
So you can calculate the duration as 6-8 sprint. And you have to decide a balanced duration to get the contract and to deliver everything in time.
With agile, it is absolutely possible to commit to a fixed scope. A fixed-scope plan answers the question of when a set of product backlog items can be delivered. Ideally a fixed-scope plan will be given as a range: “You will get that fixed scope sometime between this and that date.” Unfortunately, plans often have to be narrowed and overly specified into single-date estimates because bosses, clients, and customers prefer the false certainty of having a single date.
If you promise a delivery date based on the high end of a team’s predicted velocity range, that will be the earliest possible delivery date for the fixed scope. If you promise to deliver everything by the earliest possible date, you’ll probably meet your customer’s expectations but you run the risk of letting that customer down later when you don’t deliver everything as promised.