Why do the pros bet less than Kelly says? — Statometrics Academy calculator

Try it · Kelly growth simulator

True win chance36.0%

Believed win chance (sizes the stakes)36.0%

Decimal odds

Commission

Number of bets1,000

Starting bank (£)

Kelly fractions to compare

How many bettors

━ one bettor each━ median bank

Fraction	Stake per bet	Median final bank	Below start	Halved at some point	Median worst fall
¼ Kelly	0.84%	£3,227	9.7%	0.2%	24.2%
½ Kelly	1.67%	£4,530	14.1%	8.3%	45.3%
Full Kelly	3.35%	£5,928	20.2%	39.2%	72.2%

Full Kelly keeps 100% of the growth that staking the true full Kelly would give. The median bettor ends on £5,928, but 39% saw their bank halve along the way.

Each bettor re-sizes to their current bank after every bet. Figures come from 1,000 simulated bettors per fraction (the median bank is also worked out exactly). The chart uses a log scale, so doubling always looks the same height.