How to use this calculator
Enter the number of flips and a heads count. The default 50% describes a fair coin; change it to model a biased coin. Exactly k heads counts all arrangements with that many heads, not just a single ordered sequence. At least k includes higher counts. This tool does not calculate the chance of a streak appearing anywhere in the sequence.
The formula
P(k heads) = C(n,k) pᵏ (1 − p)ⁿ⁻ᵏ
Here p is a probability from 0 to 1, n is a whole number of attempts, C(a,b) counts combinations, and ∏ means multiply all the factors. The input labels define the other symbols.
A worked example
Exactly 5 heads in 10 fair flips has probability 24.61%. A specific 10-flip sequence has probability 1/1,024.
Does this predict what I will get?
No. It describes a probability under the rules you enter. A single run can differ from the average. A displayed rounded 100% may still be slightly below certainty unless the model includes a guarantee.
Where do the rates come from?
You enter them. Check the rules and rate disclosure for your exact outcome. We do not supply odds for real products, collect account details or fetch rates from a game or seller.