Coin Flip Probability Calculator
Find the probability of k heads in n coin flips.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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Request a ToolHow to Use the Coin Flip Probability Calculator
Enter the number of coin flips, how many heads you want, and the probability of heads on a single flip (0.5 for a fair coin). Select whether you want the probability of exactly that many heads, at least that many, or at most that many.
About This Calculator
Coin flip probability follows the binomial distribution. The probability of getting exactly k heads in n flips is C(n,k) * p^k * (1-p)^(n-k), where p is the probability of heads on a single flip. This calculator handles both fair and biased coins.
Frequently Asked Questions
What is the probability of 5 heads in 10 flips?
For a fair coin, the probability of exactly 5 heads in 10 flips is C(10,5) * 0.5^10 = 252/1024 = approximately 24.6%.
Can I use this for biased coins?
Yes. Change the probability of heads from 0.5 to any value between 0 and 1 to model a biased coin.
Why is the probability of all heads so low?
The probability of n heads in a row is 0.5^n for a fair coin. For 10 flips, that is 0.5^10 = 0.098%, or about 1 in 1024.