How it works
Start with 0 and 1, then add the previous two terms for each new term. Under this zero-based convention, F₁₀ is 55. The index is limited to 78 so the returned integer stays within JavaScript’s exact integer range.
Inputs and units
| Input | Example value | What to enter |
|---|---|---|
| Index n | 10 | Enter a numeric value. Use a whole number. Use a non-negative value. Allowed range: 0–78. |
Worked example
Show example inputs and results
This example is generated by the same calculation engine using the starting values in the form. Your own inputs produce your own result.
- Index n
- 10
Complete example results
- Fibonacci number Fₙ
- 55
Reading the result
Use quantities on the same basis. The starting value in percentage change, the denominator in a ratio and the length unit in geometry determine the meaning of the answer. Check the formula conditions alongside the example.
Questions and answers
Can I use the example values for my own calculation?
The example values illustrate the calculation. Replace every input with your own information, especially dates, rates and the selected operation.
Is the first term always assigned index 1?
No. This tool assigns 0 to index 0 and 1 to index 1, so 55 is F₁₀, the eleventh entry when index 0 is included. A list beginning with 1, 1 instead has 55 as its tenth entry. Check the starting convention before comparing positions.
Why are some results rounded?
Results display up to 8 decimal places. Calculations use the unrounded values; very small values use scientific notation. JavaScript floating-point arithmetic can introduce tiny rounding differences.
Are my inputs sent to a server?
The calculator processes inputs in your browser. Its code does not send your values to a server.