The iteration burndown report is the primary tool for understanding the status of the current iteration. It shows the trend for how much work is left to do within the iteration. This is accomplished by adding the estimated effort left for each of the Work Items to be addressed within the iteration and showing how the estimated effort is changing over the duration of the iteration. The iteration backlog should be updated frequently, preferably daily.

These factors affect the team’s assessment of how much work remains:

• Work that has been completed, which means there is less work remaining.
• The developer responsible for a Work Item changes the assessment of effort required to complete the Work Item. This should be expected, because we typically understand what it really takes to complete a task after we have done a subset of the task. It's common for estimates of the work remaining to increase in the beginning of the iteration, especially for inexperienced teams, because they often underestimate efforts. Expect estimates to continue changing as teams become more experienced, but the modifications are upward as often as downward.

Daily or frequent updates of the iteration burndown report allow the team to react to changes. For example, changes can include cutting the project scope by removing Work Items from the iteration, reducing the ambition level associated with a Work Item, or finding better ways of approaching Work Items, such as having an expert team member help with difficult Work Items.

See Iteration Burndown Report for an example of an iteration burndown report.