Fibonacci Calculator
Generate the first N Fibonacci numbers, or pick out the Nth term by itself.
First 10 Fibonacci numbers
55
The 10th term. Full sequence below.
1, 1, 2, 3, 5, 8, 13, 21, 34, 55
How it works
The Fibonacci sequence starts 1, 1, and then every term is the sum of the two before it: 1 + 1 = 2, 1 + 2 = 3, 2 + 3 = 5, and so on. It shows up in everything from spiral shells to the way rabbits breed in the classic puzzle.
Choose 'first N' to see the whole run up to your chosen length, or 'Nth term' to skip straight to a single value — the 10th term, for instance, is 55.
The calculator builds the sequence one step at a time rather than with a formula, which keeps it exact. It goes up to the 90th term, the point where the numbers pass the safe-integer limit.
Frequently asked questions
Does the sequence start at 0 or 1?
This calculator starts at 1, 1, 2, 3, 5, which is the most common convention for counting problems. Some textbooks tack a 0 on the front; if you need that version, just shift the term numbers by one.
What's the connection to the golden ratio?
Divide any Fibonacci number by the one before it and the ratio settles closer and closer to about 1.618, the golden ratio. The further along the sequence you go, the tighter that approximation gets.
Why does it stop at the 90th term?
Around the 90th Fibonacci number the values grow past the range where whole numbers stay exact. Rather than show a rounded figure, the calculator caps there so every number it prints is precise.