User Story Estimation
The Developers estimate the relative effort involved to implement the User Stories. This is an important point, because traditionally the developers have had estimates imposed on them. By 'owning' the estimates, the developers not only have a vested interest in meeting those estimates, but they also tend to make much more realistic estimates in the first place.
Each story receives an estimate of 1, 2 or 3 Points. A point is an arbitrary value that is used to perform estimates of one story relative to another. One simple method is to choose a Story and set its estimate to 2 points. Select another Story, and decide whether it's the same size and therefore 2 points as well, smaller and therefore 1 point, or larger and thus 3 points. If the developers don't feel comfortable providing an estimate to a story, it's likely because they don't know enough about it. In that case, they ask the Product Owner for more information. This can result in the developers having enough detail to provide the estimate, or that the Story may need to be split into multiple stories.
Estimation Example
This is a sample user story for defining a Customer Discount Rate:
The problem with this Story is that it's too large. There are a couple of concepts here that need to be split out into separate stories:
This provides just enough detail for everyone involved (Product Owner, Developers) to agree on the importance of the story, and for the Developers to create a reasonable estimate of the time required to implement it. It doesn’t delve into any specific details about how the system performs the action, any validations required, etc. These are left until the Developers are creating the programming tasks, and consult the Product Owner for more details.
Having said that, there still isn't quite enough detail in the Preferred Customer story. During the Release Planning meeting, the Developers would likely ask the Product Owner, "When do you start counting the $50,000?"
With the answer in hand, the Story is updated by the Product Owner, and the Developers provide their estimate:
