27 Heads in a Row on a Fair Coin
The chance of 27 heads in a row on a fair coin is 7.45 × 10-7%, or 1 in 134.22 million. Tails is exactly the same, and so is a run of any one side you pick in advance: each flip is a 50% chance, so 27 in a row is 0.5 multiplied by itself 27 times.
The odds of 27 in a row
| Measure | Value |
|---|---|
| Chance of 27 heads from a given flip | 7.45 × 10-7% |
| Odds | 1 in 134.22 million |
| Flips to wait for it, on average | 268.44 million |
| Chance of 27 heads OR 27 tails starting on a given flip | 1.49 × 10-6% |
| Chance a run of 27 appears at least once in 100 flips | 2.79 × 10-5% |
| Chance a run of 27 appears at least once in 1,000 flips | 3.63 × 10-4% |
| Chance a run of 27 appears at least once in 10,000 flips | 3.72 × 10-3% |
| Chance a run of 27 appears at least once in 100,000 flips | 0.0372% |
Why it is likelier than it feels
A run of 27 on one chosen flip is 1 in 134.22 million, yet across 1,000 flips there is a 3.63 × 10-4% chance one turns up somewhere. People judge a streak against a single starting point, but a long sequence gives it thousands of starting points. That is also why streaks in a real record of flips look suspicious to anyone who does not expect them, and why a sequence with no streaks at all looks more made-up than one that has them.
Does a streak change the next flip?
No. After 27 heads the next flip is still 50% heads and 50% tails. A fair coin has no memory, and on Cryptoflip every game's result comes from a provably fair roll that was committed to before anyone joined. Expecting the streak to "break" is the gambler's fallacy, and expecting it to continue is the hot-hand fallacy.
In Original, our player-versus-player coin flip, a game is a straight 50/50 and the winner takes the pot minus a 5% fee. See how a result is verified.