🌀 Fibonacci Calculator
Generate the first N Fibonacci numbers or compute the Nth term. Uses BigInt for arbitrary precision on large numbers.
Generate first N terms
Compute the Nth term
About the Fibonacci Calculator
This Fibonacci calculator runs entirely in your browser and uses JavaScript BigInt to handle arbitrarily large results. You can either generate the first N terms of the Fibonacci sequence or compute the Nth term directly. No data is sent anywhere — every calculation is performed locally.
Fibonacci sequence definition
- Recurrence —
F(1) = 1, F(2) = 1, F(n) = F(n−1) + F(n−2)for n > 2. Each term is the sum of the two preceding terms. - First terms — 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, …
- Growth rate — The ratio F(n+1)/F(n) approaches the golden ratio φ ≈ 1.6180339887 as n grows.
- Why BigInt — JavaScript Number loses integer precision past 2⁵³. F(79) is the largest term exactly representable as a Number; BigInt keeps every digit exact for far larger n.
How to use the calculator
- Pick the card that matches your task: a full sequence or a single term.
- Enter a positive integer N.
- Click Generate or Calculate to see the result below the button.
Frequently asked questions
What is the largest N I can use? Sequence generation is capped at 1000 terms and single-term calculation at 10000, to keep the page responsive. Both limits produce exact BigInt results.
What convention is used? F(1) = 1, F(2) = 1, F(3) = 2. The sequence therefore starts 1, 1, 2, 3, 5, 8, …
Why does the result have so many digits? Fibonacci numbers grow exponentially. F(100) has 21 digits; F(1000) has 209 digits.
Is my input stored or uploaded? No. Everything happens in your browser. Your numbers are never sent to a server.