You arrive at the sportsbook with $5,000. This is your bankroll. Your job is to make it last through good times and bad times without going broke.
The Kelly Criterion says you should bet a percentage of your bankroll on each play proportional to your edge. If you have a 5% edge (meaning you expect to win 52.5% of your bets at -110 odds) and your bankroll is $5,000, you should bet approximately 2.5% of your bankroll per play, or $125.
Most bettors use a simpler rule: 1-5% of bankroll per bet, depending on confidence. High confidence (55%+ expected win rate): 5%. Moderate confidence (52-54%): 2-3%. Low confidence (50-52%): 1%.
The Session Reality
You place ten $125 bets over an evening. You hit 6 and miss 4 (slightly above expected). Your profit is 6 * 125 - 4 * 110 = 750 - 440 = $310. You end the session with $5,310.
Now you have $5,310. Your next bet should be based on 1-5% of $5,310, which is $53-$265. Most bettors stay at $125 (failing to scale up) or increase to $200 (overconfidence). Either is fine if discipline is maintained.
The mistake: increasing to $250 per bet because you are winning, or increasing to $500 per bet because you are losing (chasing). These violate bankroll rules and accelerate ruin.
Variance and Ruin
A bettor with a 52% win rate and 1% bankroll bets has a 99.8% probability of never going broke (assuming infinite betting opportunities). The same bettor with 5% bets has a 10% ruin probability. The same bettor with 10% bets has a 50% ruin probability.
This is not opinion; this is Kelly Criterion mathematics. Higher bets generate higher variance, which means higher probability of large losses that deplete the bankroll.
Variance Blindness
Winning bettors feel invincible. The gentleman with $5,310 (up $310) is tempted to increase bet size because variance has gone his direction. This is the moment of maximum danger. Variance reversals are sudden and crushing.
Losing bettors feel desperate. The bettor down $1,000 is tempted to increase to $500 per bet to "get even." This is chasing, and it turns a manageable loss into a catastrophic one.
The Rule
Do not increase bet size after a winning streak. Do not increase bet size after a losing streak. Increase bet size only when your bankroll grows to 2x its original size. This is the only signal that your capacity has actually increased.
Key Takeaway
The key is understanding the system. Most people do not take the time. The ones who do are the ones who profit from the ones who do not.
Understanding the System
The lesson underneath all of this is the same: understand the system before you enter it. The system is designed. The odds are known. Your job is to know them too, and then decide whether the trade is worth making. Most people skip the first step and proceed directly to wondering why they lost money. The final note is that bankroll management is not about avoiding losses. It is about surviving variance long enough for your skill or luck to play out. A proper bankroll prevents you from going broke during an unlucky streak so that you can still be in the game when luck turns.
