Coin Flip
Flip a fair virtual coin once, or thousands of times, and see the heads and tails counts, the longest streak and how the share of heads settles towards 50%. Uses your browser’s cryptographic random source.
How to Use
- Set how many coins to flip: 1 for a quick decision, up to 100,000 to experiment.
- For a single flip you can call heads or tails first.
- Press Flip; press it again for a new flip.
- For many flips, read the heads and tails counts, the share of heads and the longest streak.
- The chart shows the running share of heads wobbling and then settling inside the shaded ±2σ band around 50%.
Worked Example
10 flips. Exactly 5 heads is the single most likely result, yet it happens only 252/1024 = 24.6% of the time. 4 or 6 heads together are more likely (41.0%), and 8 or more heads happens 5.5% of the time.
1,000 flips. Expect about 500 ± 16 heads (one standard deviation is √1000 ÷ 2 = 15.8), so 470 to 530 covers about 95% of runs, and a longest streak around log₂ 1000 ≈ 10.
The common mistake: expecting tails after a run of heads. After HHHHH, the chance of tails on the next flip is still exactly 50%. Streaks feel meaningful, but each flip is independent.
Show Work
Formulas
Famous Coin Flippers
The naturalist Georges-Louis Leclerc, Comte de Buffon, tossed a coin 4,040 times in the 18th century and got 2,048 heads. The statistician Karl Pearson tossed 24,000 times and got 12,012. John Kerrich, interned during the Second World War, made 10,000 tosses and recorded 5,067 heads, using them in a book on probability.
Coin tosses have decided real things: the city of Portland, Oregon, was named in 1845 when Francis Pettygrove beat Asa Lovejoy (who wanted “Boston”) two flips out of three.
About This Tool
This tool flips a fair coin using your browser’s cryptographic random source, once or up to 100,000 times. For many flips it reports the counts, the longest streak against what is typical, and how unusual the split is, and draws the running share of heads settling towards 50% inside its statistical band.
Everything runs in your browser; nothing is sent anywhere.
Related tools: Dice Roller, Random Number Generator, and Probability Calculator.
Frequently Asked Questions
Is a coin flip really 50/50?
This one is: each flip takes one random bit from your browser’s cryptographic generator. Real coins are very close but not perfect; a 2023 study of 350,757 flips by 48 people found a 50.8% chance of landing on the same side it started, because of slight wobble in the toss.
After 5 heads in a row, is tails due?
No. The coin has no memory: the next flip is 50/50 whatever came before. Believing otherwise is the gambler’s fallacy. Streaks are simply common: in 100 flips the longest run is usually 6 or 7, and a run of 6 or more happens about 80% of the time.
Why isn’t it exactly half heads?
Because random counts vary. In 100 flips the standard deviation is 5, so anything from about 40 to 60 heads is normal. The share of heads gets closer to 50% as flips add up (the law of large numbers), but the count of heads minus tails actually tends to wander further from 0.
What does the p-value of the split mean?
The chance a fair coin would give a split at least as uneven. 60 heads in 100 flips has a p-value of 0.057: unusual but not rare. If you see p below 0.01 repeatedly, something is wrong with the coin.
How long a streak should I expect?
About log₂ of the number of flips. 100 flips usually contain a run of 6 or 7, 1,000 flips a run of 9 or 10. People asked to write down fake coin flips almost never include runs that long, which is a classic way to spot invented data.
How do I use the Coin Flip?
Simply pick your options and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Do I need to install or sign up for anything?
Not at all — it runs in the browser with nothing to install and no account. After it loads once, it even works without an internet connection.
Is my information private?
Yes. Everything happens in your browser. Nothing you type is sent to a server or saved anywhere.
Common Use Cases
Decisions
Heads or tails to settle a choice or pick who goes first.
Classroom
Flip 1,000 coins and watch the share of heads settle near 50%.
Streaks
See runs of 9 or 10 in a row in 1,000 flips.
Sports
A fair toss for kick-off or serve.
Probability
60 heads in 100 flips has p = 0.057.
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