Burndown Chart Calculator

Burn-down charts answer a question that is asked at regular meetings: Can we complete the project on time if we continue to work in this way? This calculator does the calculations behind the chart. Enter the scope and duration of your sprint, along with either total or daily values, to get current velocity, required velocity, and expected completion date.

Many burn down tools just connect dots with lines. This tool calculates the ideal line, actual line, difference between them on any given day and estimated time to completion. It also accounts for scope changes after sprint start which is often hard to see in traditional burn down charts.

What is a burn down chart?

A burn-down chart is a line graph that shows the remaining work and the remaining time. Time is shown on the horizontal axis with each day of the sprint having a mark. The remaining work is shown on the vertical axis, usually measured in story points.

The chart has five elements: two axes, an ideal line that falls linearly from the full scope at the beginning of the sprint to zero on the last day, a real line which represents remaining work, and story points which define markers on the vertical axis. On a sprint that is completed as planned, both lines intersect with the horizontal axis on the final day.

The term "burn-down" has a practical meaning. In Scrum story points measure the effort, complexity and uncertainty of an item, not the time it will take. When an item is completed, its points are considered done, and the total remaining amount is reduced accordingly. Work that is incomplete is not counted as done.

The calculation basis behind the chart:

All the information shown on the chart can be generated with just four simple formulas. We denote the scope of a sprint in story points as S, the number of working days in a sprint as D, the completed working days so far as e and the completed story points so far as b.

Ideal remaining work amount:

As the ideal line is a constant downward movement, the value on day e is calculated as follows:

Current burn rate:

The rate achieved so far, expressed as a number of story points completed per day is as follows:

Required rate of removal:

This is the speed required for the rest of the sprint. It's a numerical value that serves to turn a graph into a basis for decisions.

Scheduled completion date:

At the current pace of work, remaining work will be completed by the following date.

Compare this outcome with D. If the completion is ahead of schedule, you can have earlier delivery. If it's behind schedule, then you're facing a quantifiable delay rather than vague sense of unease.

A full example.

The Alpha team has committed to completing 35 story points in a two-week sprint. A two-week sprint with five working days per week is 10 working days, not 14 days. After five working days the team has completed 15 points.

The remaining work is 20 points, calculated as the difference between 35 and 15. The remaining days are 5. The current velocity is 3 story points per day, calculated by dividing 15 by 5. The required velocity is 4 story points per day, calculated by dividing 20 by 5.

The ideal line on day 5 is half of 35 which is 17.5 points. As the team has 20 points remaining they are 2.5 points behind their ideal line. If the team maintains a velocity of 3 story points per day then the work will be completed on day 5 plus 20 divided by 3 which is 11.67 days. This equates to a sprint length of 10 days.

So an honest interpretation is not that the team is behind but one and two thirds days. The solution would be to either complete an additional story point each day or remove 5 story points from the sprint.

The ideal line can be drawn manually.

In a five-day sprint with an 80-hour workload, the daily work amount is 16 hours, calculated by dividing 80 by 5. Subtracting this value each day will give you your ideal line.

Let's say the actual hours recorded by the team on those five days were 14, 19, 16, 15 and 16. If you add these up you get 80 so your actual line must end at zero. Subtracting each day from this gives values of 66, 47, 31, 16 and 0.

It is worth checking this calculation manually. A single error can carry through to the end and cause the line to fall below zero. If the actual line eventually shows a negative number and the sum of daily values equals the planned value, then the problem lies not with the estimate itself but in an erroneous intermediate calculation.

Understanding the importance of the difference between lines

At the beginning of a sprint, these two lines are often close together; it is only after several days that enough data has been gathered to see a meaningful difference.

• Above the ideal line: This indicates that the remaining work package is larger than planned and problems are beginning to occur. The longer the line stays above this position, the higher the required speed must be.

• On ideal line - speed is on plan and task expected to be completed by final day.

• Below the ideal line: The team is working faster than planned. There may be room for additional tasks but it could also indicate that there was not enough commitment to the sprint.

• A line that falls vertically and steeply usually indicates that several tasks were done simultaneously or the scope was secretly reduced instead of being completed.

Flat lines require special attention. When the amount of work doesn't decrease over two or three days it almost always means that no one is working on anything. This usually indicates that ongoing tasks have stalled, either because of pending reviews, dependencies or missing tasks required to complete them.

Changes in scope: A blind spot on charts

Burn-down charts only show the remaining work and nothing else, so all of those descending lines look exactly the same. It doesn't matter if a team has completed five points or someone has sneakily removed five points from a sprint - it looks no different on the chart. You can't tell which is happening by looking at the chart.

For this reason, this calculation tool treats added and removed volumes as separate input points. When this adjustment is enabled, the ideal line will be redrawn based on the actual volume taken, and also the required speed reflects that change. In addition, the result panel shows the changes to the originally promised volume in percentage.

It is more important to document the change itself than just the numbers. A sprint that was completed on time despite a 20% increase in scope is fundamentally different from one where a fifth of the scope was removed to meet the deadline. Only by documenting this change can both scenarios be distinguished in retrospectives.

Points, time or number of tasks

All of the formulas do not ask for a unit to be used. As the amount of work is divided by the number of days, any consistent measure of work can be used. Story points are most common as they represent not only time but also complexity and risk.

For teams that value and track their time, timing is best. It also allows for a better understanding of productivity. Counting tasks is the most crude method and only works if the tasks are small enough and the team can reasonably complete at least one task per day.

When the effort layer is enabled, the calculator will convert between the two methods. By entering the average time per point, the actual hours worked by one person daily and the number of team members it provides the total amount of work (in hours), remaining time and the number of points that the team can actually deliver per day. When this productivity is compared to the required velocity unrealistic sprints will be apparent from the start.

What a burn-down chart doesn't show:

The graph is intentionally kept simple but this simplicity has a cost.

• All points are weighted equally. It may happen that twelve simple tasks and five difficult tasks have the same drop-off, and it is not possible to tell from this line which of them are more difficult.

• Priorities are ignored. Even if a team does the wasteful work quickly, it still looks like a team that is meeting sprint goals.

• Changes in scope will be hidden unless they are documented separately.

• All estimation errors are carried over. If an order of magnitude estimate is too optimistic, the ideal line will be too optimistic as well and the actual line just reflects that honestly.

A burn-down chart shows the decreasing amount of work remaining while a burn-up chart shows the increasing amount of work completed. By adding a total scope line it makes the scope of the work visible at a glance. These two charts are good to use together; the burn-down chart showing what is left to do, and the burn-up chart showing progress made.

Use these numbers in your regular meetings.

When you verbalize those three numbers, the discussion becomes more concrete: The remaining points, the required speed from now on and the expected completion date.

If the required velocity is within the range that can be achieved with the current velocity then confirm this and move on. If there is a large difference then a useful question to ask is not whether the team can increase their velocity but which items should be removed from the sprint and who needs this information.

The ratio of the committed scope to the actual completed scope determines your velocity. By accumulating data over multiple sprints you get a more accurate picture for planning the next sprint than any single estimate. The planning mode used here is also based on this data. If you enter a velocity that the team can actually maintain, it will calculate how many days are needed to complete the proposed scope and by what factor the committed performance is exceeded.