How this coin flip works
A coin flip is the simplest fair random choice there is: two equally likely outcomes, Heads or Tails. This tool reproduces that fairness digitally. Instead of physics, it asks your browser for random data and maps it to a side of the coin so that each outcome lands with a true 50% chance.
The randomness comes from crypto.getRandomValues, the same cryptographically strong source browsers use for security tasks. To stay perfectly unbiased the tool uses rejection sampling — it discards the rare leftover values that would otherwise nudge the odds — so there is no lean toward heads or tails. If a browser somehow lacks that generator, it falls back to Math.random.
When you flip several coins at once, the tool tallies how many came up heads and tails and shows the percentage split. It also keeps a short history of recent flips and a cumulative session counter so you can track the running totals.
Heads vs. tails odds
| Outcome | Probability | Odds |
|---|---|---|
| Heads | 50% | 1 in 2 |
| Tails | 50% | 1 in 2 |
| Two heads in a row | 25% | 1 in 4 |
| Three heads in a row | 12.5% | 1 in 8 |
Reference note: these probabilities assume a fair coin with independent flips. This tool models an ideal fair coin; a real physical coin can carry tiny biases from its minting and how it is tossed.
Frequently asked questions
- Is this coin flip truly random and fair?
- Yes. Each flip uses your browser's cryptographically strong random number generator (crypto.getRandomValues) with rejection sampling so there is no bias, giving each outcome a genuine 50/50 chance. If that generator is unavailable, it falls back to Math.random.
- How does the coin flip work?
- When you press Flip, the tool draws random bytes from your device, maps each coin to Heads or Tails with equal probability, and shows the result instantly. Everything runs locally in your browser — nothing is sent to a server.
- Can I flip multiple coins at once?
- Yes. Choose how many coins to flip — from 1 up to 100 — and the tool flips them all at once, then shows the tally of heads and tails along with the percentage split.
- What are the odds of heads?
- On a fair coin the odds of heads are 50%, exactly the same as tails. Over a small number of flips the split can look lopsided, but across many flips the totals tend toward an even 50/50.
- Is it good for decisions, games and settling bets?
- Yes. A coin flip is a quick, unbiased way to make a yes/no choice, pick who goes first, or settle a friendly disagreement. Because each flip is independent and fair, neither side has an advantage.
- Does it store my flips?
- No. The recent-flip history and cumulative counter live only in the current page session and are cleared when you reload or close the tab. Nothing is saved or uploaded.