Kelly Criterion Simulator
The coin lands heads 60.0% of the time. Choose a side, size your bet, and see what over- or under-betting the edge does to a bankroll, including asymmetric reward:risk payouts.
Study context
This setup echoes a well-known 2016 experiment by Haghani and Dewey, in which participants were given a real bankroll and a coin they were told would land heads 60% of the time, a genuine, sizeable edge. Despite that edge, a large share of players still went bust, mostly by betting far more than the edge justified, switching sides after a few losses, or chasing losses with bigger stakes. The lesson isn't just "the math has an optimum." It's how easy it is to abandon that optimum under pressure, even when the odds are known and in your favor.
This version adds an adjustable reward:risk payout so you can model asymmetric edges: low hit-rate / high payoff strategies, not just even-money coins. A 30% win rate at 3:1 can still be +EV; Kelly sizing changes with both probability and payout.
A 60% coin is generous, though. It's a teaching device. Most real trading edges are nowhere near that clean. Discipline means sizing every trade the same principled way without inflating after wins or abandoning after losing streaks. Both are ways of quietly giving up the edge you're trying to harvest.
The hardest skill isn't finding an edge. It's telling the difference between "this losing streak is just variance" and "my edge is actually gone," and behaving correctly under each.