Fibonacci Calculator
The Fibonacci sequence starts 0, 1, 1, 2, 3, 5, 8… — each term is the sum of the previous two.
Calculator
Use the Fibonacci Calculator
Result
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Formula
F(n) = F(n−1) + F(n−2)
Step-by-step
- 1
Enter the term index
F(0) = 0 and F(1) = 1.
- 2
Read the term
The nth Fibonacci number is shown.
Worked example
Example input: n: 10
Result: 55
Related tools
- Factorial Calculator
Another classic sequence.
Frequently asked questions
What is the 10th Fibonacci number?
55 — the sequence runs 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55. Each term adds the two before it, so entering 10 above returns 55 with the whole chain computed internally. The pattern reached Europe in 1202 through Leonardo of Pisa, whose nickname Fibonacci now names both the man and the series.
Where does the sequence start — 0 or 1?
This calculator uses the standard indexing F(0) = 0 and F(1) = 1, the convention mathematics and most textbooks share. Some casual lists start at 1; subtracting one index converts between them.
Why does the sequence grow so fast?
Each new term is roughly 1.618 times the previous one — the golden ratio. That multiplier compounds, so F(30) is already 832040 while F(15) is just 610: exponential growth disguised as addition.