See how close to 50/50 you actually get. Run 100 coin flips instantly, analyze the heads/tails split, longest streak, and expected deviation. Perfect for probability class or satisfying your curiosity.
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One hundred flips is where probability starts to feel real. With just 10 flips, a 7-heads result seems surprising — but with 100 flips, the Law of Large Numbers kicks in and your results reliably converge toward 50/50. Mathematically, the standard deviation of a 100-flip run is exactly 5, which means roughly two-thirds of all runs will land between 45 and 55 heads. Running this tool a few times lets you observe this distribution firsthand. If you pool 30 students' results in a classroom, the combined percentage will be remarkably close to 50% — a live demonstration of the central limit theorem without a single formula.
After each run, the streak panel shows the longest consecutive heads run and the longest consecutive tails run. Most people expect long streaks to be rare — but in 100 fair flips, a streak of 7 or more appears in roughly 80% of all runs. A streak of 6 appears in about 96% of runs. Our brains are wired to see patterns in randomness and flag them as suspicious, but long streaks are a mathematical certainty in large enough samples. The streak note tells you whether your run's longest streak is typical or on the shorter side, so you can calibrate your intuition.
With 100 flips, the expected deviation from 50 heads follows a binomial distribution with standard deviation σ = √(100 × 0.5 × 0.5) = 5. That means: getting 45–55 heads is within 1 standard deviation (68% of runs), getting 40–60 heads is within 2 standard deviations (95% of runs), and getting outside 40–60 heads — say, 37 heads or 64 heads — happens only about 5% of the time and would be considered statistically notable. The summary line after each run tells you whether your result was "very close," "within normal range," or a "notable deviation."
Statistics teachers use this tool for several core lessons. For a Law of Large Numbers demo, have each student run 3–5 trials and record their heads counts — then aggregate the class totals and watch the percentage converge toward 50. For a Gambler's Fallacy lesson, have students predict the next flip after a long streak, then reveal that each flip is always exactly 50/50 regardless of history. For a standard deviation lesson, collect all students' heads counts and plot them — you'll get a nearly perfect bell curve centered on 50 with spread of about 5, without any simulation software required.