Toss a Coin
Flip a coin online for heads or tails. It is fair, it is free, and nothing you do here leaves your browser.
The toss
Press Toss. The face is drawn on the press; the coin hangs at the top long enough to call it.
The draw happens before the coin is in the air
Pressing Toss does three things in order. First the engine draws random bits from crypto.getRandomValues, the browser's cryptographically strong random source, seeded with entropy collected by your operating system. Second, it maps them onto heads or tails by rejection sampling — drawing the minimum number of bits that covers the range and discarding any draw that falls outside it, so neither face can be even fractionally favored. Only third does the coin move, spinning a number of half-turns whose parity is chosen to land on the face already drawn.
That order is the whole design. The alternative — simulating a spinning disc and reading whichever face happens to be up when it stops — sounds more honest and is less so, because the result then depends on floating-point arithmetic, frame timing, and whatever constants the author picked, none of which has been measured for bias. Here the flight length varies genuinely from toss to toss, but that variation is drawn independently of the face, so a long tumble tells you nothing about how it will land.
Real coins are not quite 50/50
A tossed physical coin does not rotate cleanly about a single axis; it precesses, which keeps the launch face up slightly more of the time than geometry alone would suggest. Careful empirical work on this — including a very large study in which volunteers recorded hundreds of thousands of real flips — has found a small but consistent same-side bias, on the order of a percent rather than anything dramatic. It is far too small to notice over a handful of tosses and far too small to matter for deciding who buys lunch, but it is real, and it is the one thing a browser can genuinely do better: with no physical coin and no launch face, there is nothing for the bias to attach to.
Catching the coin versus letting it land, spinning a coin on a table instead of tossing it, and worn coins with uneven faces all introduce larger effects than the toss itself. If you want the fairest physical procedure, have one person toss and a different person call.
Two ways to call it, both legitimate
Call before the flip is the formal convention: the call is on the record before the coin moves, which removes any argument about what was said and when. Leagues that run a supervised pregame toss work this way — the visiting captain calls, then the referee flips.Call it in the air is the older, more theatrical convention, still standard in cricket and on every playground: the coin goes up, and you call while it is turning. This page supports both because both are real, and because the fairness argument is identical either way — the outcome is fixed the moment the toss begins, so calling later cannot change it.
Your call accuracy appears in the tally. Over a long session it will sit near 50%, which is the point: there is no skill in calling a fair coin, and watching your own numbers refuse to beat chance is a better argument than any amount of prose.
What a fair coin actually looks like
Fair coins produce streaks. A run of five or six identical results is not evidence that something is broken — it is a statistical near-certainty over a few hundred tosses, and the tally tracks your longest run so you can watch it happen. The corollary is the part people get wrong: because every toss is independent, a coin never "owes" you tails. After six heads the next toss is 50/50, exactly as it was before the first one. That intuition — that a result is "due" — is the gambler's fallacy, and it is the most expensive misunderstanding in probability.
Prefer a coin that looks like a coin?
This one is built to be read instantly: two metals, and each face carries its own name. If you would rather have the ritual — an actual 1878 Morgan silver dollar, Liberty on the obverse and the eagle on the reverse, where you recognise the side instead of reading it — the Real Coin Toss runs the same draw underneath, with the same call modes and the same tally.
Frequently asked questions
Is this fairer than tossing a real coin?
Measurably, yes. A physical coin toss has been found to carry a small same-side bias — the face that starts up lands up slightly more often than half the time, because a tossed coin precesses rather than rotating cleanly about one axis. This coin has no launch face to favor: heads and tails each come from one cryptographically random bit with exactly equal probability, drawn before the animation starts.
Does the animation decide the result?
No, and that ordering is deliberate. Pressing Toss draws the face first; the engine then reports the exact rotation that shows that face, and the flight decelerates onto it. Nothing about the tumble, the hang time, or when you call it can change the outcome. A physics simulation would work the other way round — the landing would emerge from floating-point arithmetic whose bias nobody has measured.
If the result is decided before I call it, is calling in the air still fair?
Yes — and it is fair for exactly the same reason a real coin toss is. The outcome is already determined the moment the coin is in the air; you are calling something you cannot influence and cannot see. Your call is recorded against the draw, never fed into it, so a called toss and an uncalled toss run identically.
Why do official sports tosses call before the flip?
Because calling in the air invites disputes about whether the call was made in time and what was actually said. Calling before the coin is flipped puts the call on the record first, which is why leagues that run a formal pregame toss have the visiting captain call before the referee flips. Cricket keeps the older convention, where the call is traditionally made while the coin is up.
Heads came up six times in a row — is it broken?
No. That is what fair randomness looks like: six in a row has roughly a 1-in-64 chance and will happen regularly if you toss often enough. Each toss is independent, so after six heads the next toss is still exactly 50/50. The tally under the coin shows your longest run for this reason — watching streaks arrive at about the expected rate is the most convincing fairness demonstration there is.
Does anything I do here leave my device?
No. The draw, the tally, and the history all run in JavaScript on your own device. There is no server application to send them to, nothing is logged, and closing the tab discards the session.
Games and tie-breaks only: fair enough for who goes first, not a certified randomness source for wagering or anything auditable. Everything runs locally in your browser — how the draw is implemented and tested is documented on the methodology page. Need more than two outcomes? Spin a wheel at SpinThatWheel.net.