Why estimate with the Fibonacci sequence

The Fibonacci sequence is the one where each number is the sum of the two before it: 1, 2, 3, 5, 8, 13, 21, 34 and so on. It became the default planning poker deck for a practical reason: the gaps grow along with uncertainty.

The gaps represent uncertainty

Small stories are easy to compare. A team can tell whether something is a 2 or a 3. For large stories, that precision disappears. Nobody can reliably tell a 20 from a 21, but they can tell a 13 from a 21.

With Fibonacci, options are spaced further apart exactly where estimation error is largest. That prevents debates that go nowhere and forces the team to admit when a story is too big to estimate with confidence.

Big numbers are a warning

When a story gets 21, 34 or more, the team's message is clear: split it. Many teams agree on a ceiling, say 13, and anything above that goes back to refinement before entering a sprint.

Modified Fibonacci

Modified Fibonacci replaces the high values with round numbers and adds a half point: 0, ½, 1, 2, 3, 5, 8, 13, 20, 40 and 100. It helps when:

• the backlog mixes tiny tasks with entire epics;
• the team wants a way to say "this is almost nothing" with ½;
• 21, 34 and 55 feel like false precision and 20, 40 and 100 convey the order of magnitude better.

Points are not hours

Fibonacci points measure relative size: effort, complexity and risk combined. Converting points to hours throws away the technique's advantage, because it demands precision where none exists again. The team's velocity, measured in points per sprint, bridges to the calendar far more honestly.

How to calibrate your team

1. Pick a delivered story everyone remembers well.
2. Agree that it is worth 3 points.
3. Estimate the next ones by comparing with that reference: smaller, similar or bigger?
4. Revisit the reference every few months, when the team changes or the product matures.

In StoryPoints

The Fibonacci deck is selected by default when you create a room. Modified Fibonacci, T-shirt sizes, powers of 2 and custom decks are one click away in the settings. On reveal, StoryPoints calculates the average, median and agreement and suggests the deck value closest to what the team had in mind.