Factorial Calculator

Calculate factorial (n!), double factorial (n!!), and subfactorial (!n) for any positive integer. Includes permutation and combination formulas.

What is Factorial Calculator?

This factorial calculator computes n! for any non-negative integer (up to very large values), along with double factorial, subfactorial (derangements), and the Gamma function for non-integers. Shows the step-by-step multiplication chain.

How to Use This Calculator

  1. Enter your n (max 20), r (for nPr, nCr) in the input fields provided
  2. Results are computed instantly as you enter or modify values — no need to click a button
  3. Review the computed output showing your factorial results with a detailed breakdown
  4. Cross-check the output with your manual working to reinforce the underlying concept

How Factorial Calculator is Calculated

This calculator implements standard mathematical formulas for factorial operations. Computations follow established mathematical principles from standard textbooks. Results are precise to the level of JavaScript floating-point arithmetic.

Frequently Asked Questions

What is factorial used for?

Factorials count arrangements (permutations). 5! = 120 means 5 items can be arranged in 120 different ways. Used in probability, combinations (nCr = n!/r!(n-r)!), Taylor series, and statistical distributions.

How fast do factorials grow?

Extremely fast. 10! = 3,628,800. 15! = 1.3 trillion. 20! = 2.4 × 10¹⁸. 52! (deck of cards arrangements) = 8 × 10⁶⁷ — more than the estimated atoms in the observable universe.

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Reviewed by Sagar Sahni
Founder & Lead Developer, Calc Labz · Last verified May 2026

Why Use This Calculator?

Accurate mathematical computation is the foundation of problem-solving across science, engineering, and everyday life. Factorial Calculator provides instant, step-by-step solutions using validated algorithms. Whether you are a student preparing for JEE, NEET, or board exams, a professional verifying calculations, or a researcher needing quick computation, this tool eliminates manual errors and shows the complete solution methodology.

What This Tool Offers

  • Instant Factorial Calculator calculation with validated formulas
  • Detailed step-by-step result breakdown
  • Works offline as a Progressive Web App
  • Completely free — no signup or data collection
  • Mobile-friendly responsive design
  • Save and share your results easily

Expert Tips

  • 💡 Verify your understanding by working through the step-by-step solution shown.
  • 💡 Practice with different values to build intuition about how the formula behaves.
  • 💡 For competitive exams, learn the shortcuts alongside the standard method.
  • 💡 Cross-verify with manual calculation for critical applications.
  • 💡 Bookmark for quick access during study sessions — works offline too.

Who Is This For?

Students preparing for JEE, NEET, and board exams, mathematics teachers creating worksheets, engineers and scientists needing quick computation, and anyone working with numbers.

📚 Complete Guide Available

Want to learn more? Read our comprehensive guide with detailed explanations, real-world examples, expert analysis, and actionable tips.

Read: Factorial

Note: This calculator provides results based on standard mathematical formulas. Always verify important calculations independently.

Maintained by: Sagar Sahni, Calc Labz  |  Review: formula checks, worked examples, and periodic updates

Need a correction? Contact us with the calculator name, your inputs, and the issue you found.

Last updated: April 2026