Probability Calculator

Calculate probabilities, combinations (nCr), permutations (nPr), factorials, coin flip and dice odds, and Bayes' theorem. 100% client-side.

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Enter favorable outcomes and total outcomes.

How to Use the Probability Calculator

  1. Select a calculation mode: Basic, Combinatorics, Coin/Dice, or Bayes.
  2. Enter the required values for your calculation.
  3. Results appear instantly with formulas and explanations.

Calculators Included

  • Basic probability: favorable events / total outcomes
  • Combinations (nCr): choosing r items from n without order
  • Permutations (nPr): arranging r items from n with order
  • Factorials: n!
  • Coin flip probability for exact number of heads
  • Dice roll probability for target values
  • Bayes' theorem: posterior probability calculation

Disclaimer:This tool is provided “as is” for informational and educational purposes only. Results may not be 100% accurate. ToolBird makes no warranties, express or implied, regarding the accuracy, reliability, or completeness of any output generated by this tool. This tool does not constitute professional, legal, financial, medical, or tax advice. Always consult a qualified professional for important decisions. By using this tool, you agree that ToolBird and its operators shall not be held liable for any damages, losses, or consequences arising from the use of this tool or reliance on its results. All processing occurs in your browser — we do not store, transmit, or access your data. Use at your own risk.