Coin Flip
Heads or tails? Flip one coin to settle a decision, or flip a hundred at once to watch probability play out — with a running tally of how close your session gets to 50/50.
Session flips
0
Heads
—
0 total
Tails
—
0 total
Each flip is an independent 50/50 draw from crypto.getRandomValues — a virtual coin has no same-side bias, unlike a hand-flipped physical coin, which lands on its starting side about 50.8% of the time (Bartoš et al., 2023, from 350,757 recorded flips).
Why the Coin Has No Memory
Each flip is independent: after five heads in a row, the next flip is still exactly 50/50, because the coin carries no memory of past results — believing otherwise is the gambler's fallacy. What makes a streak feel special is its advance probability: before you start, the chance of five heads in a row is 1/2⁵ = 1/32 ≈ 3.1%. But once those five heads have happened, they have no pull on flip six. Over many flips the heads percentage drifts toward 50%, yet short sessions swing wildly — 10 flips land exactly 5–5 only about 24.6% of the time.
Streak odds (fair coin)
2 heads in a row 1/4 25% 3 heads in a row 1/8 12.5% 4 heads in a row 1/16 6.25% 5 heads in a row 1/32 3.125% 10 heads in a row 1/1024 ~0.1% Every individual flip stays 50/50 — streaks change nothing about the next toss.
Frequently Asked Questions
After five heads in a row, is tails more likely next?
No — the next flip is still exactly 50/50. Each flip is independent; the coin has no memory, and believing a result is 'due' is the gambler's fallacy. What was unlikely was the streak in advance: five heads in a row has a 1/32 ≈ 3.1% probability before you start, but once it's happened it tells you nothing about flip six.
Is a real coin toss actually 50/50?
Almost, but not quite — a 2023 study of 350,757 recorded flips (Bartoš et al.) found coins land on the same side they started about 50.8% of the time, due to wobble in the toss, confirming a physics prediction by Diaconis. A virtual flip from crypto.getRandomValues has no starting side, so it's exactly 50/50.
What are the odds of exactly 5 heads in 10 flips?
About 24.6% — there are C(10,5) = 252 ways to arrange 5 heads among 10 flips out of 2¹⁰ = 1,024 equally likely sequences, so 252/1024 ≈ 0.246. Counterintuitively, a perfect 50/50 split is the single most likely outcome yet still happens less than a quarter of the time, which is why short sessions swing far from 50%.
How many flips does it take to tell if a coin is biased?
Far more than intuition suggests. Detecting a 51/49 bias reliably takes on the order of 10,000 flips; even after 100 flips, a fair coin will land outside 40–60 heads about 5% of the time just by chance. The session tally here shows the law of large numbers in action — the percentage creeps toward 50% but rarely sits exactly on it.