Coin Flip Streak Tracker
Flip coins and track streaks of heads or tails. Useful for probability experiments.
About this calculator
Flip coins and track the current and longest streak of heads or tails.
A fair, instant way to settle a choice, and a small probability lab.
How to use it
- Press Flip! repeatedly.
- Watch the streak counter.
- Press Reset to start over.
The maths of coin flips
A fair coin lands heads with probability 1/2 on every flip, independent of earlier flips. In n flips, the expected number of heads is n/2, but the actual count varies: the standard deviation is √n/2. In 100 flips, heads between 40 and 60 happens about 95% of the time. The chance of a streak of at least k in a row grows with the number of flips: in 100 flips, a run of 6 or more of the same side is more likely than not.
Worked example
Probabilities
| Heads on one flip | 50% |
| Two heads in a row | 25% |
| Five heads in a row | 3.125% (1 in 32) |
| Ten heads in a row | about 0.098% (1 in 1,024) |
Tips and common mistakes
- Past flips do not affect the next one (the gambler's fallacy).
- Small samples vary a lot; 10 flips can easily be 7-3.
- Use 'best of 3' for fairness.
- Calling before the flip avoids disputes.
- Longer runs of the same side are normal in long sequences.
Frequently asked questions
Is the flip fair?
Yes, 50% each.
Is a streak of 5 heads unusual?
Not in many flips: 1 in 32 for any given 5.
Does the coin remember?
No, each flip is independent.
What is the gambler's fallacy?
Believing a streak makes the opposite more likely.
How many heads in 10 flips?
On average 5, but 3 to 7 is typical.
Is it free?
Yes.