Why Modified Fibonacci Sequence Works for Agile Estimation

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 Agile teams may struggle with precise time estimates, leading to missed deadlines and stressed team members. That's where the Modified Fibonacci sequence comes in - a practical solution that has changed how teams approach estimation.

What is the Modified Fibonacci Sequence?

Ever wondered why Agile teams don't just use regular numbers for estimation? That's where the Modified Fibonacci sequence comes in. Let's break it down in simple terms.

The Modified Fibonacci sequence used in Agile looks like this: 0, 1, 2, 3, 5, 8, 13, 20, 40, 100

Notice how these numbers get farther apart as they get bigger? That's not an accident - it's actually one of the most powerful features of this system.

The traditional Fibonacci sequence (where each number is the sum of the previous two) looks like this: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89...

However, Agile teams modified it to make it more practical. Why? Because when estimating larger tasks, it's harder to tell the difference between similar numbers. Think about it - can you really tell the difference between a 34-point story and a 35-point story? Probably not!

When Should You Use Fibonacci Agile Estimation?

Timing is everything when adopting new estimation techniques. Fibonacci estimation works best when your team needs a fresh approach to sizing work items - but how do you know when that time has come?

The perfect time to implement Fibonacci estimation is usually when you're starting a new project. Your team can start fresh, without any old estimation habits getting in the way. It's like learning to drive - it's easier to learn good habits from the start than to break bad ones later.

But don't worry if you're in the middle of an ongoing project. Many teams successfully switch to Fibonacci estimation when they notice these signs:

• Constant debates about the exact hours needed for tasks

• Missed deadlines despite detailed time estimates

• Team members feeling pressured about time commitments

• Difficulty planning sprints accurately

Is Your Team Ready?

Before jumping in, make sure your team is prepared for the change. You'll have the best success when:

• Team members are open to trying new approaches

• There's basic understanding of Agile principles

• You have at least 3-4 team members

• Your projects involve varied task sizes

However, you might want to wait if:

• Your organization strictly requires hour-based estimates

• The team is brand new to Agile concepts

• Most of your work involves simple maintenance tasks

Why Use the Modified Fibonacci Sequence in Estimation?

Let's talk about why this sequence makes such a difference in real-world projects. The benefits go way beyond just having a different set of numbers to use.

Think about how you describe the size of everyday things. You don't say a cat weighs exactly 4.3 kg - you say it's bigger than a rabbit but smaller than a dog. That's relative sizing, and it's exactly what makes Fibonacci estimation so powerful.

Here's what makes it work:

• Natural growth patterns match how complexity increases

• Bigger gaps between higher numbers reflect increasing uncertainty

• Forces meaningful choices between sizes

• Encourages breaking down large tasks 

How to Use the Fibonacci Scale in Agile

The most popular way to use Fibonacci estimation is through Planning Poker. It's a simple but effective group estimation technique. Here's how it works:

1. Product Owner reads the user story and answers any questions

2. Each team member gets a deck of cards with Fibonacci numbers

3. Everyone chooses a card secretly based on their estimate

4. All cards are revealed simultaneously

5. Discuss any big differences (like if someone says 3 and another says 13)

6. Repeat the voting if needed until the team reaches a consensus

Many teams use online planning poker tools for remote sessions. They work just like physical cards but are faster and more convenient!

Simple Rules to Follow

• If estimates vary widely, let the highest and lowest estimators explain their thinking

• If discussion takes more than 5-10 minutes, save the story for later

• Stories estimated at 20+ points should probably be broken down

• It's okay to skip complex stories and come back to them later

Final Words

The Modified Fibonacci sequence helps teams reach a common understanding on estimates without needing exact numbers. Using relative sizes rather than precise hours leads to better discussions, clearer decisions, and more consistent results.

To get the most out of this method, stay flexible and adjust as needed rather than following strict rules. Start with a single project, adapt it to suit your team, and see how it improves your estimation process. The sequence itself is just a guide—it’s your team’s collaboration that makes it effective.

[Stephen_Lugton]

@Liam - DevSamurai did you know that the number of petals on many flowers is usually a Fibonacci number (or at least averages out to a Fibonacci number)?

• lilies and iris have 3 petals,
• buttercups have 5 petals,
• some delphiniums have 8,
• corn marigolds have 13 petals,
• some asters have 21,
• whereas daisies can be found with 34, 55 or even 89 petals

[Liam - DevSamurai]

TIL! Thank @Stephen_Lugton, really interesting information 😁

Fibonacci number does appear a lot in nature