The Fibonacci sequence, where each number is the sum of the two before it, gives planning poker a scale with widening gaps. Those gaps force teams to make meaningful distinctions and stop them from arguing over false precision on large, uncertain work.
The idea behind the widening gaps
A common planning poker deck uses one, two, three, five, eight, thirteen, and twenty-one. Small items sit close together, but the distance between larger numbers grows quickly. This mirrors reality: the bigger a task is, the less confident anyone can be about its true size.
Because there is no card between eight and thirteen, the team cannot waste time debating whether something is a ten or an eleven. It picks the nearest honest bucket and moves on, which keeps estimation fast.
How to vote with Fibonacci cards
Each person selects a card privately, everyone reveals at the same time, and the team discusses any large spread. A jump from three to thirteen is a signal that people understand the work very differently, which is exactly the conversation estimation should surface.
When votes are close, the team simply agrees on a number. When they disagree, the discussion usually uncovers a hidden requirement, a dependency, or an assumption worth writing down before the work starts.
When to split instead of estimate
Cards like thirteen and twenty-one are often a warning rather than an estimate. A story that large is hard to plan, hard to review, and likely to spill across a sprint boundary.
Many teams treat anything above eight as a prompt to break the work into smaller stories. Smaller items estimate more accurately, flow through the board faster, and give clearer progress signals.
Frequently asked questions
Why not just use one to ten?
A linear scale invites endless debate over neighboring numbers. Fibonacci gaps remove that noise by making the team choose between clearly different sizes.
What does the question mark card mean?
The question mark signals that someone does not have enough information to estimate. It is a prompt to clarify the story before voting again.
Is Fibonacci better than T-shirt sizing?
Neither is universally better. Fibonacci gives more granularity for backlog planning, while T-shirt sizing is faster for early, high-level triage.