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October 06, 2023

Scrum basics: Understanding Sprint burndown chart

Project Management Reporting Scope
Agnieszka Sienkiewicz

Data-based visual apps can improve the efficiency and effectiveness of Agile teams using Scrum. For starters, team members can use story points to estimate user stories and, ultimately, their effort for Sprint. You, in turn, can use those points to define and track key Scrum metrics, including your team’s velocity and burndowns.

In this post, we’ll cover a Sprint burndown chart — what it is, how it works, and what the limitations of this tool are.

What is the Sprint burndown chart in Scrum?

A burndown chart is a graphic representation of two factors: the amount of work your team has already completed in a given Sprint, and the amount of time that the team has left to complete that work. 

You can express the amount of work using story points. (If you use a number of tasks or non-relative units like hours in your Agile planning, then you can also plot them on a burndown chart.) The burndown chart timeline, by contrast, usually shows days (which can be calendar dates or just ordered numbers). For example, you could plot days 1 to 10 for a 2-week Sprint (excluding weekends).

Who updates the Sprint burndown chart?

The Sprint Burndown chart isn’t strictly required in Scrum, so the Scrum Guide doesn’t offer guidance on how to use it. That might leave you wondering who should be responsible for updating it. The Sprint burndown chart is a tool for the Development team to communicate and track their own progress. Those team members are in a much better position to do this because they’re closest to the work. 

That’s why the developers themselves typically update the Sprint burndown. An added benefit of letting your devs manage the burndown chart is that they keep a close eye on their own progress.

But you and your team might decide to appoint someone else to facilitate the burndown charts, depending on how you work. Whomever you task with doing it, you ideally want the chart updated after every Daily Scrum meeting.

What is the purpose of the Sprint burndown chart?

The Sprint burndown chart shows the overall and day-to-day team’s progress toward the goal. It will help you predict how likely is your team to complete the work they’ve committed to in a current Sprint. (You can apply the same approach to track progress on Epics, Releases, or the entire product as well.) 

Because a burndown chart measures the progress of a specific amount of work over time, it will help you notice red flags about progress inconsistencies or scope creep.

For example, if the team regularly completes their work ahead of time, it might be a sign that they’ve underestimated user stories. And the reverse is also true — if team members consistently deliver less than they’ve initially estimated, it could indicate they took too much work into the Sprint. 

The Sprint burndown chart is a highly valuable visual for tracking the progress of your team members as they work through their user stories.

The anatomy of the Sprint burndown chart

Burndown charts are plotted based on the Cartesian plane, where work and time are two separate dimensions. The trend lines spanning across these two axes represent the actual progress and estimated (ideal) states respectively. Take a look at the example below.

An example of a Sprint burndown chart.

Time: the X-axis

The horizontal axis (X-axis) represents the Sprint timeline, indicated by the start and end dates of the work period. When using a burndown chart to track epics or releases, you can customize the timeline accordingly. For example, rather than using individual Sprint days, you would input consecutive Sprint numbers. 

Effort: the Y-axis

The vertical axis (Y-axis) represents effort, which you can measure using relative or nonrelative units of work like story points or hours. This dimension gauges your team’s progress, with the Y-axis height determining the starting point for your trend lines. For instance, if your team plans for a 40-story point initial Sprint backlog, the lines will originate from 40 on the Y-axis. 

Trend lines: actual effort vs. estimated effort

Along these two dimensions, you’ll typically find two trend lines descending from the top left to the bottom right.

The first line is the estimated effort line, which represents the ideal burndown; it shows a linear progression based on your timeline and work estimates (story points, hours, issue count, etc.). In other words, this line visualizes the best-case-scenario rate of your team’s progress. You can think of it as a baseline because any deviation from it will tell you how the team is doing with their work.

The actual effort line represents your team’s real progress rate, which is based on actual work items that your team manages to complete. This line changes every time someone updates the chart, as the team moves along the timeline.

How to read the Sprint burndown chart

First of all, it’s called “burndown” for a reason. The Sprint burndown chart plots the ideal (estimated) progress as a downward slope, gradually “burning down” to signify the project’s completion. In other words, your team “burns down” tasks, hours, or story points as they move along the timeline.

You read (analyze) the chart by comparing the actual effort trend lines to the baseline (estimated effort line). The closer these two lines align, the higher the likelihood that the team will complete all tasks on schedule.

Common shapes of the actual effort trend line.

Examining the relationship between these lines reveals key insights about Sprint progress:

  1. On track: When the estimated and actual effort lines are close or overlap, it suggests that the team is on course to meet its goal as long as it maintains its current velocity.
  2. Ahead of schedule: If the actual effort line is below the estimated effort line, it means the team has completed more Sprint tasks than originally estimated. They might even reach the goal before the Sprint ends, often due to task overestimation.
  3. Behind schedule: When the actual effort line is above the baseline, it indicates that the team is burning down Sprint tasks at a slower rate than anticipated. This could lead to missing the goal on time, typically because the team underestimated their stories.

Whether your team is on track or not is the primary information you can read from your Sprint burndown chart. But you can draw more information than that by looking at the trend line patterns.

4. Incorrect updates or overestimation: If the actual effort trend line resembles a staircase, it might suggest that tasks were not detailed enough. As a result, the team takes longer to complete them.

This shape of a trend line could indicate overestimation or incorrect updates of the Sprint burndown chart.

It could also indicate inconsistency or errors in chart updates. 

 5. Plateau: A straight actual effort trend line may suggest a temporary setback within the team, possibly caused by poorly defined user stories or unexpected resource unavailability.

A plateau pattern of the actual effort trend line.

Scope creep: When the actual effort line consistently fluctuates and veers above the baseline, it often indicates scope creep. This becomes evident when additional stories are introduced to the Sprint, leading to an increase in the workload.

Here, the actual effort line could indicate the scope creep.

Sprint burndown chart: A valuable project tracker

The Sprint burndown chart is a simple, yet powerful tool for tracking project progress, particularly in time-critical projects. By comparing ideal and actual effort over time, the burndown chart provides a practical measure of the team’s accomplishments in the Sprint. And because it offers clear insights into the remaining work, the chart also helps Scrum teams stay organized, self-motivated, and aligned towards their common goal.