About coin flipping
A fair coin flip is the simplest possible random event, with a 50% probability of heads and 50% of tails on each toss. Over a large number of flips, the tally should approach an even split, but individual sequences can deviate significantly from 50/50.
This tool uses the browser's cryptographically secure random number generator so each flip is truly independent and cannot be predicted. The running tally is useful for games, decisions, statistical demonstrations and teaching the law of large numbers.
How do you calculate coin flip probability?
The probability of any single fair coin flip landing on heads or tails is exactly 50% (1/2) each, since there are two equally likely outcomes. Example: the chance of getting heads twice in a row is 0.5 x 0.5 = 0.25, or 25%.
Steps to calculate coin flip probabilities
- Identify how many flips are in the sequence you want to calculate.
- For a single flip, the probability of heads (or tails) is always 1/2.
- For independent flips in a row, multiply the probability of each individual outcome together.
- For "at least one heads in n flips," calculate 1 minus the probability of all tails.
- Compare the theoretical probability to your actual running tally after flipping multiple times.
Coin flip probability formulas
P(heads) = P(tails) = 0.5 · P(exact sequence of n flips) = 0.5^n · P(at least one heads in n flips) = 1 - 0.5^n
- n = the number of coin flips in the sequence
- 0.5^n = the chance of one specific exact sequence, such as all tails
Example flip probabilities
| Number of flips | At least one heads |
|---|
| 1 | 50% |
| 2 | 75% |
| 3 | 87.5% |
| 5 | 96.9% |
| 10 | 99.9% |
Frequently asked questions
If I get 5 tails in a row, is heads "due" on the next flip?
No — this is the gambler's fallacy. Each flip is independent, so the probability of heads on the next flip is still exactly 50%, regardless of how many tails came before. Past flips have no memory or influence on future ones.
Why doesn't my tally show exactly 50/50 after flipping many times?
With a small number of flips, random variation can push the tally noticeably away from 50/50. As the number of flips grows very large, the proportion of heads typically converges toward 50%, an effect known as the law of large numbers, though the raw difference in count can still grow.
Is this tool's coin flip actually fair?
Yes. It uses the browser's cryptographically secure random number generator rather than a simpler pseudo-random function, so each flip has an unbiased 50/50 chance and cannot be predicted or manipulated.
What is the chance of getting the exact same result 3 times in a row?
The probability of any one specific sequence of 3 flips, like heads-heads-heads, is 0.5 x 0.5 x 0.5 = 0.125, or 12.5%. This is different from asking about "at least one heads," which has a much higher probability.
These probabilities describe an idealized fair coin and independent flips; the results shown are for illustration and educational use, not for real-money wagering or high-stakes decisions.
Sources: MDN — Crypto.getRandomValues()
Privacy and safety
- Runs in your browser — Everything you type is calculated on your own device. Your inputs are never sent to a utilduck server.
- Encrypted connection — Pages are served over HTTPS, so nobody on the network can read what you load.
- Not shared with third parties — Your inputs are not passed to analytics or advertising services.
- Nothing is stored — Results are not saved to any server, and there is no account to create.
Last updated: 2026-08-17