What is a burndown chart? Estimation of task completion time

The Burndown Chart allows you to assess the stage of completion of the current Sprint or the entire project being worked on by the Scrum Team. But most importantly, it shows how much time is needed to achieve the Sprint Goal or Product Goal. To some extent, it also enables you to measure changes in the effectiveness of the Development Team. And thanks to that, it is possible to assess the probability of finishing the tasks on time. This is because the Burndown Chart shows how much work has already been done and how much remains.

What is a Burndown Chart?

A Burndown Chart serves to estimate the time and effort needed to complete a task. It is also a valuable warning tool if the work does not go as planned. With a single glance, each Scrum Team member is able to assess the status of the tasks. Therefore, the Burndown Chart should be easily accessible to everyone involved in the project.

The Burndown Chart in Scrum features in two versions: as a Sprint Burndown Chart and as a Project Burndown Chart. We will discuss them together because the principle behind them is identical. They differ only in the time scale and the number of tasks they depict.

What does a Burndown Chart look like?

On the Burndown Chart, the X-axis shows the time remaining to complete the work. If the chart is for a Sprint, the time is measured in days. On the other hand, if the Burndown Chart is for an entire project, time is usually measured in Sprints.

The Y-axis of the Burndown Chart indicates the amount of work remaining. Thus, it refers to the tasks included in the Sprint Backlog or the Product Backlog. The units used on the vertical axis of the chart can be:

Story Points – which you can read more about in the text on User stories
Man Days/Hours
Tasks

The Burndown Chart typically includes a burn-down line that represents a perfect, linear decrease in the number of tasks that remain to be completed. It provides an outlook on the projected completion time.

Estimation of task completion time

Each Developer individually needs to estimate the number of hours they need to complete a particular task. And the estimated time to complete a Sprint Goal or Project is the sum of time estimated by all Developers. The immense difficulty is to translate the estimated time into the actual time of task execution. This is one of the major problems newly formed Development Teams face It can distort the picture presented on the Burndown Chart.

Moreover, it is not always possible to create an optimal workflow in a Development Team. As a result, task execution may suffer from downtime, which increases the task completion time.

One of the indicators of Team maturity is the ability to accurately estimate the work time. The more predictable, the more mature the team is. This is reflected in the burn rate graph, where the line reflecting real burn rate descends steadily to zero. However, this formulation does not apply to all situations.

As we wrote in the article about the statistics monitored by Scrum Master, much depends on the nature of the project itself: its innovation and the repetitiveness of the tasks performed by the Developers. The burndown chart works best for projects where the scope of work is fixed and known. Therefore, in case of innovative projects it is better to use other ways of measuring team effectiveness.

Summary

The Burndown Chart works well as a basic progress metric for most Development Teams. It is a tool to visualize the workload and time required to achieve a Sprint Goal or Product Goal. Because of its clarity and accessibility, the Burndown Chart allows all Scrum Team members to assess, in real time, where the project work is at.

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Author: Caroline Becker
As a Project Manager, Caroline is an expert in finding new methods to design the best workflows and optimize processes. Her organizational skills and ability to work under time pressure make her the best person to turn complicated projects into reality.
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