Burndown Chart Calculator (ideal line, burn rate & projected finish)

Understanding the burndown chart calculator — concept and principle

This calculator gives the key numbers behind a sprint burndown chart: the ideal work remaining today, how far ahead or behind you are, the actual and required burn rates, and the projected finish day at the current pace. Scrum masters and agile teams use it in stand-ups and sprint reviews to see early whether the sprint goal is still realistic.

How it is calculated

• Ideal remaining = total work × (1 − days elapsed ÷ sprint length)
• Ideal burn rate = total work ÷ sprint length
• Actual burn rate = (total work − remaining) ÷ days elapsed
• Projected finish = days elapsed + remaining ÷ actual burn rate
• Burn rate needed = remaining ÷ (sprint length − days elapsed)
• Days over or under = projected finish − sprint length

Work can be in story points or hours; days are working days.

The principle

A burndown chart plots work remaining on the vertical axis against time. The ideal line runs straight from the total at day 0 to zero on the last day, assuming an even pace. The actual line shows what really happened. Extending the average pace so far is a simple linear forecast: if the team keeps burning at the same rate, the remaining work will be finished after remaining ÷ rate more days. If work is added mid-sprint, remaining work can rise; a burnup chart with a separate scope line shows that more clearly.

Worked example

Defaults: 80 points, 10-day sprint, 6 days elapsed, 40 points remaining.

1. Ideal remaining = 80 × (1 − 6 ÷ 10) = 32.
2. Behind ideal by 40 − 32 = 8 points.
3. Ideal burn rate = 80 ÷ 10 = 8 per day; actual = (80 − 40) ÷ 6 = 6.67 per day.
4. Projected finish = 6 + 40 ÷ 6.667 = 6 + 6 = day 12, which is 2 days over.
5. Burn rate needed = 40 ÷ 4 = 10 per day.
6. Status: Behind — will overrun at the current pace.

How to read the result

If the needed rate is far above anything the team has achieved, adjust scope with the product owner rather than hoping for a late sprint. A small lag early in the sprint is common, because work often finishes in batches near the end. A flat line for several days usually signals blocked work or tasks that are too large to show progress.

Common mistakes

• Counting partly done stories as burned; burn only finished work.
• Using calendar days instead of working days.
• Ignoring scope added mid-sprint.
• Treating the projection as a promise; the pace is rarely constant.

Frequently asked questions

What is the difference between a burndown and a burnup chart?

A burndown shows work remaining falling to zero; a burnup shows work completed rising toward a scope line, which makes scope changes visible.

Can I use hours instead of story points?

Yes. Use the same unit for total and remaining work.

Why is my burndown flat at the start?

Teams often start several stories at once and finish them later, so little is marked done in the first days.

Sources: Agile Alliance, Agile Glossary, "Burndown Chart"