Flip a Coin
Heads or tails? Tap the coin for a single fair toss, or flip up to 10,000 coins at once and see how close the results land to 50/50 — with the longest streaks and the exact probability of a split that lopsided.
Tap the coin or the button to flip.
Flip Many Coins at Once
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Is an Online Coin Flip Fair?
Each toss here draws one bit from crypto.getRandomValues(), the browser's cryptographically secure random source, so heads and tails each have probability exactly 1/2 and every flip is independent of the ones before it. A physical coin is actually slightly less fair: studies of real tosses find a small bias toward landing on the same face it started on.
What to Expect When You Flip Many Coins
The number of heads in n fair flips follows a binomial distribution with p = 0.5. Its center and spread are:
Expected heads = n × 0.5
Standard deviation = √(n × 0.5 × 0.5) = √n / 2
Typical longest streak ≈ log₂(n)
The law of large numbers says the share of heads approaches 50% as n grows, but the count of heads can drift further from n/2 in absolute terms. With 100 flips the share usually lands between 40% and 60%; with 10,000 flips, between 49% and 51%.
Worked Example: 100 Flips
You flip 100 coins and get 58 heads. Is that suspicious?
- Expected heads: 100 × 0.5 = 50. Standard deviation: √100 / 2 = 5.
- 58 is 8 heads above 50, or 8 ÷ 5 = 1.6 standard deviations.
- The exact binomial probability of 58 or more heads, or 42 or fewer, is about 13.3%.
Roughly one run in eight is at least that uneven, so 58 heads is ordinary luck. Only when that probability drops below about 5% — 61 or more heads in 100 flips — would a statistician start to question the coin. The coin flip probability calculator computes these odds for any number of heads.
Streaks Are More Common Than You Think
People asked to write down a "random" sequence of 100 flips rarely include a run longer than four, yet a real sequence of 100 fair flips has a longest run of about six or seven. Flip 100 coins above and check the longest run — spotting missing streaks is a classic way teachers tell invented data from genuine coin tosses.
Frequently Asked Questions
What are the odds of heads or tails?
Exactly 50% each on every flip. Past results do not change the next one: after five heads in a row, the chance of heads on the sixth flip is still 50%. Believing otherwise is called the gambler's fallacy.
How many heads should I get in 100 flips?
On average 50, but exactly 50 happens only about 8% of the time. About 95% of the time the count falls between 40 and 60 heads. Use the Flip Many Coins panel above to try it yourself.
Can I use this coin flip to make a decision?
Yes. Each toss is a fair 50/50 draw from a cryptographically secure random source, so it is at least as fair as a physical coin. Assign heads and tails to your two options before you flip.
What is the probability of getting 10 heads in a row?
(1/2)^10 = 1/1,024, or about 0.098%. But in a long sequence of flips, a run of 10 somewhere is not rare: in 1,000 flips the chance of seeing at least one run of 10 heads is around 38%.
Why is the share of heads not exactly 50% after many flips?
Randomness produces fluctuation. The share of heads converges toward 50% as you flip more, but the typical gap shrinks only in proportion to 1/√n. With 10,000 flips you should still expect to be off by about half a percentage point.
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