Fraction Kelly

[brewer]

Is this preferred over full Kelly as we never really know the true probability and with Kelly it is worse to bet too much than too little?

If any of you guys use fraction Kelly what fraction do you use and why?

[Dark Horse]

Playing around with the numbers and my own comfort level I came up with these personalized values.
I would -conservatively- set 60% as the maximum attainable winning expectation for any system (even though that is not true), and bet 1/3 Kelly. That would mean that, at -105 odds, any betting
system of 60% or higher would automatically result in a 6% bet size. If I never bet anything with
a lower winning expectation than 54%, and always bet at -105 odds, that would give me seven
bet sizes:

54% - 1.89%
55% - 2.58%
56% - 3.26%
57% - 3.94%
58% - 4.63%
59% - 5.31%
60% and above - 5.99%

The difference per percentage point is roughly 0.7% of bankroll:
6.0 - 5.3 - 4.6 - 3.9 - 3.2 - 2.5 - 1.8.

If my expectation was between 58% and 57%, I would take the lower of the two.

For comparison, for full Kelly a 54% winning expectation would produce a 5.68% (!) bet size
(with -105 odds). That may work for some, but not for me.

======================================

If my maximum bet size was not 6% but 5% of bankroll, then I would simply use 2.0 - 2.5 - 3.0 -
3.5 - 4.0 - 4.5 - and 5.0 % of bankroll for winning expectations 54% through 60+%.

[u21c3f6]

I use half-kelly. I did not like the wilder swings in bankroll when using full kelly. Through trial and error I settled on half-kelly. The smoother curve fits my relatively conservative style better.

Joe.