Coin Flip Simulator

Flip virtual coins and analyze probability, streaks, and runs

Flip Configuration

0.50

Help

What is a Fair Coin?

A fair coin has exactly 50% probability of landing on Heads and 50% on Tails. Each flip is independent - previous results don't affect future flips.

Key principle: The coin has no memory. Past flips don't influence future outcomes.

The Gambler's Fallacy

The gambler's fallacy is the mistaken belief that past random events affect future probabilities.

Example: After 5 heads in a row, many people think tails is "due" - but the next flip still has exactly 50% chance of heads!

This simulator helps visualize this concept by tracking streaks and showing that unlikely runs happen naturally in random sequences.

Streaks and Runs
  • Streak: Consecutive identical outcomes (e.g., HHHH is a 4-heads streak)
  • Run: Any sequence of consecutive identical outcomes
  • Expected behavior: In 100 flips, expect to see runs of 5-7 in a row
  • Surprising fact: Long streaks are more common than intuition suggests
Biased Coins

A biased coin has unequal probabilities for heads and tails. Real coins can be slightly biased due to:

  • Weight distribution (design asymmetry)
  • Wear and damage
  • Flipping technique

Use the bias slider to simulate unfair coins and see how bias affects long-term proportions.

Law of Large Numbers

As the number of flips increases, the proportion of heads approaches the true probability (0.5 for fair coin).

Important: This doesn't mean short-term runs "balance out" - it means the percentage gets closer to 50%, not that the count difference gets smaller.

Example:

  • 10 flips: 7H, 3T (70% heads) - not unusual
  • 1000 flips: 520H, 480T (52% heads) - closer to 50%
  • 10000 flips: 5020H, 4980T (50.2% heads) - very close to 50%
Applications
  • Decision Making: Fair, random choices between two options
  • Sports: Determining possession, serve, etc.
  • Education: Teaching probability and statistics
  • Gaming: 50/50 chance mechanics
  • Cryptography: Generating random bits
  • Simulation: Binary random processes
Statistics Explained
  • Heads/Tails Count: Total number of each outcome
  • Proportion: Percentage of each outcome (should approach 50% for fair coin)
  • Longest Streak: Maximum consecutive identical flips
  • Number of Runs: How many streaks occurred
  • Average Run Length: Mean streak length
  • Alternations: How often the result switched (H→T or T→H)