Burndowns: understand the maths

The Burndown is part of the Agile Dashboard module of Urban Turtle application platform.

Why a Burndown ?

The main purpose of this graph is to monitor an iteration progress and see the remaining story points or hours to be worked to meet the sprint goal.


Story Points Burndown

The Story Points Burndown Graph allows the product owner and the Agile team to visualize the progress of an iteration in terms of business value completion. It is composed of three main metrics; the ideal trend, the completed story points and the projected trend.

Interpreting the graph

It is important to remember that story point estimation is not precise and that completion of story points can be erratic within an iteration. This graph is useful as an indicator, but a less than ideal trend on the graph does not necessarily mean that an iteration is coming off the rails any more a very optimistic trend assures a premature completion of work. This is especially true in the early days of an iteration.

Ideal Trend Line

The ideal trend indicates the pace at which the features should be completed in order to achieve the iteration goal at a steady pace. While expressed as a straight line, neither the product owner nor the team should expect the completion rate to follow this line. The team will most likely not complete the work at such a steady pace, simply because iteration items do not all have the same size and challenges can, and frequently do occur mid­iteration. The ideal trend is used as a reference to measure the gap between the actual completion rate and an ideal reference point.

Completed Story Points Line

The completed story point line indicates how many story points are completed over time. As previously stated, this line is unlikely to be as straight as the ideal trend, but it should be somewhat close to it. A large deviation could indicate that too much work has been included in the iteration, or that the estimation was off and the team and the product owner should decide together what to do to achieve the iteration goal.

Projection Line

The projection line will appear three days into the iteration. This line projects where the completed story points line is likely to be at the end of the iteration based on current rate of advancement. Since the stories vary in size and complexity, a team working on a large story at the very beginning would give a false impression of slow progress and low probability of success. Use this projection as a basis for discussing sprint progress with the team and understand if the trend is due to planned or unforeseen reasons.

Hours Burndown

The hours burdown allows the team to have a visual cue of their progress in the same way as the story points burndown does, but at the hours level. It uses the same three metrics over time, except that the measurement is in hours. Because it is common practice to update the estimated remaining hours to complete a given task, this graph is more likely to follow the ideal trend in a well planned, predictable iteration. Keep in mind that the previously stated advice about graph accuracy applies to this graph as well! Do not get misled by incomplete or early information!

What about backlog modifications during the sprint?

The graph will adjust whenever you make modifications to the iteration content. If you add work mid iteration then you will see the completed story point line rise as the work increases. Similarly, taking work out of an iteration while it is in progress will cause the completed story point line to drop.

There is an exception to this case. If you to remove work from an iteration on the last day of the iteration, those items will be counted as not completed and so the completed line will not descend to zero. Urban Turtle considers that all work removed from a sprint on or after the last day of the iteration was incomplete and will forever show as incomplete on the burndown graph for that iteration.

It is also important to understand that the ideal trend line will start at a value equal to the first day of the iteration where there are estimated values. This means that if your iteration starts on Monday but the backlog only gets filled with tasks on the next day, then the ideal trend will start from the point represented by Tuesday's estimated work remaining. 


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