Bayes' Coin Game

An interactive game to build your intuition about evidence and belief updating.

Part 1: The Betting Game

The coin is biased. Its chance of landing Heads is either 80% or 20%. Can you figure it out in 15 flips?

Trial: 1 / 15

Chips: 100

Bet on Heads:

Bet on Tails:

H

T

Place your bets and flip the coin!

You finished with chips.

Based on the results, what do you think the probability of Heads was?

Estimated P(Heads): 0.50

Update your beliefs about the coin's bias with each new flip.

Trial: 0 / 15

Last Flip:

H

T

Choose your starting assumption for the coin's bias. Click a button to select a prior, then click 'Start' to begin.

After 15 flips, your final belief about the coin's bias is shown below. The true bias was .

This chart shows how the average of your belief distribution changed with every flip.

This chart shows how your belief in each possible bias changed with every flip.