Coin Flip

A fair coin flip, on demand

This is a free online coin flip for settling a choice, kicking off a game or demonstrating probability. Tap the button and the coin spins, then lands on heads or tails. You can flip one coin or up to 100 at once, and a running tally shows how your results add up. It runs entirely in your browser: nothing is sent to a server, there's nothing to install and you don't need an account.

How to use this tool

Is a coin flip really 50/50?

In theory, yes: a fair coin has two outcomes that are equally likely, so each flip is independent and the odds are one in two every time. A coin that has just landed on heads five times in a row is no more likely to land on tails; that belief is the gambler's fallacy. Streaks are normal. In 100 fair flips, a run of six or more of the same side is actually quite likely.

Real, physical coins are a slightly different story. A 2007 analysis by Persi Diaconis, Susan Holmes and Richard Montgomery argued that a coin flipped in the usual way, spinning about a horizontal axis, has a small built-in tendency to land on the same face it started with, roughly 51% rather than 50%. A large 2023 preprint by Bartoš and colleagues, based on hundreds of thousands of recorded flips, reported a similar effect of about 50.8%. The bias is tiny, depends on how the coin is tossed and is not something you would notice in a few flips, but it shows that a hand toss is not mathematically perfect. These findings concern physical coins and human tosses, not this tool.

How this digital flip works

Each flip asks your browser's cryptographically secure random number generator (crypto.getRandomValues) for a random byte and uses a single bit of it: 1 means heads, 0 means tails. Because exactly half of the possible values map to each side, there is no rounding or modulo bias, and the result doesn't depend on how long the animation runs. The coin animation is purely visual and the outcome is decided before it spins. We don't use Math.random. Keep in mind that a fair generator still produces uneven stretches: over a small number of flips the percentages will wobble around 50% and only settle as the total grows.

When to flip a coin

• Decisions: choosing between two equal options such as where to eat. If you feel disappointed by the result, that tells you which one you actually wanted.
• Sports and games: deciding who kicks off, serves first or picks sides.
• Tie-breakers: splitting a draw in a club vote, raffle or board game.
• Classrooms: flip 100 coins, then 10 more times, and compare how close each batch gets to 50%. It's a quick demonstration of the law of large numbers.

It is meant for casual choices and teaching. Don't rely on any online tool for gambling, legal or other high-stakes decisions.

FAQ