Bankroll Management – Part I
Bankroll management is arguably the most important concept to understand to maximize your chances of success (or rather, minimize your chances of failure).
Did you know that with a $1,000 bankroll and a model with a 55.0% winning percentage, if you bet $100 per game at -110 lines, you would go broke ~14.0% of the time after 100 bets? After 1,000 bets the chances of you going broke are a more staggering ~31.0%.
Why does this happen? Despite a positive expected value, you’re betting too much. And this gives you a high risk of ruin.
The Kelly Criterion states that 5.5% of your bankroll is the ideal wager size to maximize the median return of your portfolio. So, what if we bet $55 instead, which represents 5.5% of our bankroll. What’s our risk of ruin then?
After 100 bets? ~2.0% After 1,000 bets? ~13.0%.
Better, but still significant risk of ruin.
Some might be surprised to see any risk of ruin at a 5.5% bankroll allocation. One of the assumptions, however, that the Kelly Criterion relies on is that bet sizes are a percentage allocation of your portfolio and not a fixed amount. Among sports bettors, a fixed bet amount is frequently referred to as a bet “unit”.
Bet Units vs Bet Allocation
Record: 72-53 +13.7 units
Patriots -7.5 2 units
Sports bettors love to measure their performance or display their picks as a function of “units”. Most people use it and because of its widespread adoption, it’s easy to communicate between parties. Since it’s become the de facto unit of measurement for sports bettors, it is widely accepted that the best way to practice bankroll management is to 1) determine your wager size and 2) never deviate from that bet size.
Let me explain the risks behind that strategy and why Cleat Street doesn’t recommend it.
Flat Betting $55: Expected Value of 1,000 Bets
We all know how to calculate the expected value, or EV, of a single bet. All you need is three inputs:
1) Payoff of a win (Pw): $50
2) Payoff of a loss (PL): -$55
3) Probability of winning (p): 55.0%