Flip a coin

How to use the flip a coin

1. Tap Flip, tap the coin itself, or press the space bar.
2. Watch the coin land on heads or tails.
3. To flip several coins at once, choose how many under Coins. Your running tally and longest streak appear below.

Is an online coin flip really 50/50?

Yes. Each flip has exactly a 1 in 2 chance of heads and a 1 in 2 chance of tails, and every flip is independent of the last one. flipj uses your browser's built-in cryptographic random number generator (crypto.getRandomValues), the same source browsers use for encryption keys. We also avoid "modulo bias", a subtle flaw where some results come up slightly more often than others. Every result is generated on your device, so nothing you enter is sent to us.

A real coin is very slightly less fair. Researchers who filmed hundreds of thousands of tosses found real coins land on the side they started on about 51% of the time. Our virtual coin has no starting side, so it doesn't have that bias.

Streaks are normal

Flip a coin 20 times and there's roughly a 3 in 4 chance you'll see a run of at least four heads or four tails in a row. People often think streaks mean something is wrong, but they're exactly what real randomness looks like. The coin has no memory: after five heads in a row, the next flip is still 50/50.

Ways to use a coin toss

• Settle a decision, like who goes first, who pays or which film to watch.
• Sports kick-offs, when you don't have a coin to hand.
• Teaching probability: flip 100 coins at once and see how close to 50 heads you get.
• Breaking a tie between two equally good options. If you feel disappointed by the result, that tells you which one you really wanted.