Coin flip guide
Why Does a Coin Land on Heads or Tails?
A real coin has two broad faces and a narrow edge. The heads-or-tails model simplifies a physical experiment with more possible behavior.
Flight and landing differ
Release sets the coin’s initial position, orientation, and rotation. Catching a coin ends the experiment differently from letting it hit a surface and bounce. The procedure is part of the experiment’s definition.
An edge is possible
A coin can rest on its edge. Research on edge landings models the geometry and dynamics of the tossing experiment. No single edge probability applies to every coin, surface, and release; this page does not assign one.
A face is not universally 50/50
An ideal symmetric model is useful for calculation. A physical experiment also depends on starting conditions and the catching or landing method. Same-side tendencies in caught tosses do not establish a fixed heads advantage for every procedure.
Digital flips have no edge state
Quick Coin Flip selects one of two labels from evenly sized groups of random values. Its animation illustrates that selection; it does not predict the trajectory or landing of a real coin.
Sources and further reading
- Probability of a tossed coin landing on edge — Physical Review E (1993)
- Dynamical Bias in the Coin Toss — Diaconis, Holmes and Montgomery (2007)
Worked examples use the independent fair-coin model unless a section explicitly discusses physical tossing.