Coin flip — heads or tails, genuinely 50/50
Flip a coin — or a hundred at once — with a genuinely 50/50 cryptographic flip, a running tally, and the heads percentage as it converges.
Runs entirely in your browser — nothing is uploaded.
All processing happens in your browser. Your file is never uploaded.
Each flip is an independent 50/50 draw from the browser's cryptographic generator. The running tally is there to watch the law of large numbers do its thing: short runs of several heads in a row are completely normal, and the percentage only settles near 50% over many flips. Past flips never influence the next one — the gambler's fallacy is believing otherwise.
How to use
- Flip. One coin for a decision, many for an experiment.
- Read the result. Heads or tails, with each coin shown.
- Watch the tally. The running percentage drifts toward 50% as flips accumulate.
Questions
Is this really 50/50?
Exactly 50/50, from the browser’s cryptographic generator — which is more than can be said for a physical coin: studies of real coin flips find the side facing up at launch lands up about 51% of the time, because of precession in the toss.
I got five heads in a row. Is it broken?
No — runs are what genuine randomness looks like. Five heads in a row has a 1-in-32 chance on any five flips, so it happens regularly. Each flip is independent: after five heads, the next flip is still exactly 50/50. Feeling that tails is now “due” is the gambler’s fallacy.
Why does the percentage settle near 50% but the counts drift apart?
The law of large numbers guarantees the ratio converges, not the difference. After 10,000 flips a gap of 100 between heads and tails is normal — that is a 1% difference in share — and the absolute gap typically grows with the square root of the number of flips even as the percentage tightens.
Can I use this to decide something important?
A coin flip is a time-honoured tie-breaker precisely because it is incorruptible and instant. There is also a real psychological trick in it: if the result disappoints you, you have just learned what you actually wanted — at the cost of one flip.