The Optimal Burndown Line (a downward-sloping line) is a visual representation on the Burndown Chart that illustrates the rate at which your team should be completing work in the Sprint Backlog (measured in Story Points) if they are to achieve delivery of the Sprint Goal.
The Optimal Burndown Line
The steepness of the slope is determined by the total number of points versus Sprint duration. If for example; the total estimation of Story Points in your Sprint Backlog amounts to 32 points and your Sprint is two weeks in duration, then the Optimal Burndown Line would represent the total amount of work in Story Points evenly distributed over the 10 working days (3.2 points per day) of your Sprint. If your team can complete (burndown) Sprint Backlog Items at the optimal rate, they will complete all planned work by the end of the Sprint.
Reference Point
The Optimal Burndown serves as a reference point for your team to assess their actual against planned progress. Deviations from the optimal burndown will highlight if the team is ahead, behind schedule or on track.
A significant early deviation below the optimal burndown might indicate an overestimation of points assigned to user stories in the Sprint, the appearance that the team is progressing faster than expected can then subsequently lead to potential overcommitment in future sprints, conversely, a deviation above the line might suggest delays or challenges that need to be addressed. As a general rule of thumb, for a 2-week sprint, aim for an average story point size of 5, with 8 as the maximum.
Adjustments and Adaptations
Use the optimal burndown to make adjustments during the Sprint. If you are happy with the size of the stories but the team are progressing ahead of schedule, you might want to consider bringing forward work earmarked for the next sprint. If the team are behind, they may need to reprioritise or place greater emphasis on addressing impediments. The team can use the Optimal Burndown to assess their progress, discuss then implement any necessary adjustments that may be needed to achieve the Sprint goal.