Coin Flipper

What the Coin Flipper Does

Press the button and the coin lands on heads or tails, each with a one-in-two chance. A tally underneath counts your heads and tails as you go, so you can watch the split over many flips.

It is the quick way to make a fifty-fifty decision, settle a dispute, or demonstrate probability — no physical coin required, and it never rolls under the sofa.

How It Works

Each flip draws a random value and calls it heads if the value falls in the lower half and tails otherwise, giving each side an exact one-in-two chance. The tally adds one to whichever side came up.

Every flip is independent of the last. The coin has no memory, so after five heads in a row the next flip is still an even fifty-fifty — the results only tend toward an even split because, over many flips, the average settles near one-half, not because the coin corrects itself.

Generation algorithm

1. Flip. Draw a random value when you press the button.
2. Decide the side. Call it heads if the value is in the lower half, tails otherwise — an even 50/50.
3. Update the tally. Add one to the side that came up.
4. Show the result. Display heads or tails and the running counts.

Each flip

Each side has an exact one-in-two chance, and every flip is independent of the last.

Technical Details

Standards & references

• Even 50/50 — heads and tails each have a one-in-two chance; the split is exact because the random value is equally likely to fall in either half.
• Independent flips — each flip stands alone; previous results do not change the odds, so a side is never 'due' — the gambler's fallacy.
• Pseudo-random source — flips come from the browser's Math.random, fine for casual use but not cryptographically secure, so not for gambling or security.

Accuracy & Limitations

Each flip is an exact fifty-fifty and is independent of every other flip. A run of heads does not make tails more likely next time — believing it does is the gambler's fallacy.

Over many flips the proportion of heads tends toward one-half. That is the law of large numbers, and it works by averaging out over a large number of flips, not by the coin 'correcting' a recent imbalance.

It uses the browser's pseudo-random generator, which is fine for settling a choice or teaching probability, but it is not cryptographically secure — do not use it for gambling or anything where the outcome must be unpredictable to others.

The tally counts your flips in this session only. Refreshing the page resets the counts; nothing is saved.

A short run of flips can look lopsided — several heads in a row is normal and expected in random data. The even split only emerges over many flips.

Real-World Use Cases

When to use it — and when not to

Need to pick among more than two options? Use the random name picker or the random number picker. Need unpredictable randomness for security? Use a cryptographic generator, not this one.

Frequently Asked Questions

References

• Gambler's fallacy (Wikipedia)
• Law of large numbers (Wikipedia)
• Math.random() (MDN Web Docs)

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