What is the Modified Fibonacci Sequence?

The modified Fibonacci sequence is a variation of the traditional Fibonacci sequence, specifically designed for agile estimation. While the standard Fibonacci sequence goes 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144..., the modified version used in agile is:

0, 1, 2, 3, 5, 8, 13, 20, 40, 100

Why Use Modified Fibonacci Instead of Standard Fibonacci?

1. Better Scale for Story Points

The modified sequence provides a more practical scale for story point estimation. The gaps between numbers increase as the numbers get larger, acknowledging that larger stories are harder to estimate precisely.

2. Includes Zero Point Stories

The addition of 0 allows teams to identify stories that require minimal effort or are already completed. This is particularly useful for tracking small improvements or quick fixes.

3. More Manageable Upper Range

The modified sequence caps at 100, encouraging teams to break down large stories rather than assigning extremely high point values. This leads to better sprint planning and more accurate estimates.

How to Use Modified Fibonacci in Planning Poker

Step 1: Understand the Scale

Each number in the sequence represents a relative level of effort:

• 0: Minimal effort, already done, or quick fix
• 1: Very simple task, minimal complexity
• 2: Simple task, well understood
• 3: Straightforward task, some complexity
• 5: Moderate complexity, clear requirements
• 8: Complex task, some uncertainty
• 13: Very complex, significant uncertainty
• 20: Extremely complex, high uncertainty
• 40: Epic-level complexity, consider splitting
• 100: Too complex to estimate, must be split

Step 2: Create Reference Stories

Establish a set of reference stories for each number in the sequence. These should be well-understood stories that your team has completed before. Use these as benchmarks for future estimation.

Step 3: Use in Planning Poker

During planning poker sessions:

1. Present the user story to the team
2. Allow time for questions and discussion
3. Each team member selects a number from the modified Fibonacci sequence
4. Reveal estimates simultaneously
5. Discuss any significant differences
6. Reach consensus on the final estimate

Best Practices for Modified Fibonacci Estimation

1. Keep Stories Small

If a story is estimated at 20 points or higher, consider breaking it down into smaller stories. This improves both estimation accuracy and delivery predictability.

2. Use Question Mark (?) Card

Include a question mark card for stories that need more information before they can be estimated. This is especially useful when using the modified Fibonacci sequence.

3. Add Coffee Break (☕) Card

The coffee break card signals that the team needs a break or that the current discussion is going too long. This helps maintain team engagement during estimation sessions.

Common Mistakes to Avoid

• Don't convert points to hours - The modified Fibonacci sequence measures relative complexity, not time
• Don't skip the discussion - Understanding differences in estimates is crucial for accurate estimation
• Don't estimate alone - Modified Fibonacci estimation is a team activity
• Don't ignore the scale - Use the full range of numbers appropriately

Tools for Modified Fibonacci Estimation

Modern planning poker tools like EstimateIt make it easy to use the modified Fibonacci sequence. Look for features like:

• Built-in modified Fibonacci scale (0, 1, 2, 3, 5, 8, 13, 20, 40, 100)
• Customizable estimation scales
• Reference story management
• Team-based estimation views
• No registration required for quick setup

Conclusion

The modified Fibonacci sequence is a powerful tool for agile estimation that acknowledges the increasing uncertainty in larger stories. By using this sequence in your planning poker sessions, you'll get more accurate estimates and better sprint planning.

Remember, the goal isn't mathematical precision—it's achieving team consensus on relative complexity. The modified Fibonacci sequence provides just the right framework for these crucial conversations.