Flip a Coin

What this coin flipper does

It flips a fair coin — once, a hundred times, or as a best-of series that runs until one side takes the majority. You can rename the two sides for any two-way decision, watch the running tally, see every individual flip, and export the whole sequence.

Each flip is an independent 50/50 draw. Unlike a physical coin, which can be very slightly biased by its minting and by how it is thrown, this one is uniform by construction.

How the flip works

Every draw on this page starts with crypto.getRandomValues, the cryptographically strong random source built into your browser. That is a CSPRNG seeded from operating-system entropy: unpredictable in practice, and the right choice when a result decides something that matters. It is deliberately not described as “true randomness”, which would require a physical entropy source such as atmospheric noise or radioactive decay. Tools that claim true randomness from a browser are overstating what the platform provides.

A coin flip needs a single random bit, which is the simplest possible case: draw a random value and take it modulo two. Because two divides evenly into 2³², this particular case has no modulo bias — though the same shortcut applied to a six-sided die would introduce it, which is why the shared engine uses rejection sampling throughout.

Streaks, and the gambler’s fallacy

The single most common misunderstanding about coin flips is the belief that a run of heads makes tails “due”. It does not. The coin has no memory, no mechanism for tracking history, and no tendency to correct. After ten heads in a row, the next flip is still exactly 50/50.

What actually happens over many flips is not correction but dilution: early imbalance is swamped by later flips rather than reversed. Ten extra heads in the first hundred flips is a 10% skew; the same ten extra heads after ten thousand flips is 0.1%. The absolute difference never has to shrink for the proportion to approach half.

Best-of series

Set a best-of number and the tool flips until one side reaches the majority — first to three in a best of five. The series can therefore end in three, four or five flips, and the tool reports both the winner and how many flips it took.

This is a better model than flipping a fixed number of times when you are settling something: the series stops as soon as the result is decided, exactly as a real best-of contest does. It also illustrates a point worth knowing — a best-of-five is not meaningfully “fairer” than a single flip for a fair coin. Both give each side exactly 50%. Longer series reduce variance for a biased coin, not for a fair one.

Worked example: a hundred flips

Flip a hundred times and you will typically see something like 47/53 rather than 50/50. That spread is normal: the standard deviation for a hundred fair flips is five, so results between 45 and 55 cover the great majority of outcomes.

Flips     100
Heads     53  (53.0%)
Tails     47  (47.0%)
Longest run: 6 heads

A 53/47 split is unremarkable. So is 44/56.

Renaming the sides

The two sides can be anything: two restaurants, two candidates, two dates. The tally, the flip list and the CSV export all use your labels, which makes the record readable afterwards — “Thai 6, Italian 4” is more useful in a group chat than “Heads 6, Tails 4”.

Practical uses

• Settling a two-way choice where both options are acceptable and the deliberation has stopped adding value.
• Deciding who goes first in a game, an interview order, or a presentation slot.
• Teaching probability — a hundred or a thousand flips demonstrates the law of large numbers, streaks, and the gambler’s fallacy far better than explanation alone.
• Simulating binary events at scale, with CSV export for analysis elsewhere.

Limitations

Up to 1,000 flips per run, and best-of series up to 21. The bias control exists for teaching and simulation — set it away from 50% and the flip is deliberately unfair, with a warning shown so it cannot be mistaken for a fair coin.

Privacy

Flips are generated in your browser and never transmitted. The history stays in the page and disappears when you leave or clear it.

Related tools

The Yes or No Generator answers the same 50/50 question in words rather than sides. The Dice Roller covers outcomes with more than two faces, and the Random Number Generator handles arbitrary ranges. For choosing between more than two named options, use the Wheel Spinner or Random Item Picker.