Need a quick, neutral way to make a 50/50 decision? An online coin flip is perfect for settling small choices, picking who goes first in a game, running classroom demos, testing simple probability ideas, etc.
Result
Ready
The result updates the moment the coin lands.
History (last 20)
How reliable is the randomness?
Fairness check: 10,000 tosses
Run a large batch and see how evenly Heads and Tails distribute. This does not affect your normal flips.
How this coin toss works behind the scenes
A fair coin flip is just one random bit: 0 or 1. This is a good coin flipper because it uses the Web Crypto random generator, which gets unpredictable random data from your device’s operating system and then converts that into a Heads or Tails result. That’s the same class of randomness used for security-sensitive tasks in the browser, so for a simple 50/50 outcome it’s about as solid as browser-based randomness gets.
Coin toss probabilities you can actually use
For a fair coin, each flip is independent. That means the chance of getting Heads (or Tails) on any single flip is 1/2, and the chance of a specific streak of the same side happening k times in a row is:
(1/2)k
- 2 in a row (HH or TT): 1/4 = 25%
- 3 in a row: 1/8 = 12.5%
- 4 in a row: 1/16 = 6.25%
- 5 in a row: 1/32 = 3.125%
- 6 in a row: 1/64 = 1.5625%
So yes, streaks feel dramatic, but they’re normal. Even a 1.6% event shows up pretty often if you flip enough times.
Fun facts about streaks and “coin flip psychology”
- The gambler’s fallacy: If you see Tails five times in a row, the next flip is still 50/50. The coin has no memory.
- Streaks are expected: In a long run of flips, you will almost certainly see runs of 4, 5, or more. Your brain treats it as “rare,” but large samples make rare things show up.
- Close to 50/50 does not mean perfectly even: After 100 flips, being off by 6 to 10 is not weird at all. Randomness naturally wiggles.
- “Fair” does not mean “alternating”: Many people expect HTHTHT… but true randomness often has clumps.
What should you expect over many flips
As the number of flips grows, the share of Heads tends to drift toward 50% and the share of Tails tends to drift toward 50% as well. It won’t be perfectly even at every moment, but over time it usually gets closer. That’s a core idea in probability called the law of large numbers.
Ideas for using a coin toss in real life
- Fast choices: pick between two options when you’re stuck
- Games: decide who starts, which team picks first, or which side plays which role
- Classroom demos: teach independence, streaks, and why “random” does not look “neat”
- Content and challenges: add a “Heads means do X, Tails means do Y” rule for videos or posts
Sources
- MDN: Crypto.getRandomValues() – how browsers provide cryptographically strong random values.
- W3C: Web Cryptography API (WebCrypto) – official specification for the Web Crypto API.
- IETF RFC 4086: Randomness Requirements for Security – why weak randomness is risky and what “good randomness” means.
- NIST SP 800-90A Rev. 1 random bit generation concepts used in secure systems.
What is your scenario of using this tool? Need any features added to it? Share in the comments below!
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