Is Flipping a Coin Really a 50-50 Proposition?

Flipping image via Shutterstock

Don't bet on it. In 2004, three statisticians from Stanford and UC Santa Cruz set out to test the classic coin flip. Using a mechanical flipper to ensure identical tosses, they chucked thousands of coins into the air and landed on a surprising conclusion. For a hand-tossed coin, there's a slight bias toward the side it started on landing face up. While the bias only means the coin lands same-side-up 51 percent of the time, that's still a better bet than anything you'll find in a casino.

If the coin spins when it lands, the odds shift some more. Depending on the coin's design, even a slight weight advantage on one side may increase the odds of heads or tails. The trick is picking the right coin, since the U.S. Mint has issued nearly 100 different coin designs (including state quarters and presidential dollars) over the past 15 years.

This article originally appeared in the January-February issue of mental_floss magazine.