The 5% Bankroll Rule: Why Most Players Go Broke in the First 90 Minutes
If you bring $500 to the casino and play $25/hand blackjack, the math says you have a 73% chance of going broke in two hours. The 5% rule is the simplest fix.
The 5% bankroll rule: never risk more than 5% of your trip bankroll on a single session, and never bet more than 1% of your session bankroll on a single hand. If you have $1,000 for a 3-day Vegas trip, that's $50/session ÷ 100 hands = $0.50 per hand. Sounds tiny. It's correct. Most players bet 5-10% per hand and go broke fast.
The math of casino bankroll is unforgiving. The shorter the session, the more variance dominates skill. A game with a 1% house edge and 3% standard deviation per hand will, in 100 hands, produce a result anywhere from -25% to +20% of total wagered with 95% probability.
In English: you can play perfect blackjack and still lose 25% of your bankroll in two hours through pure variance. If your session bet is too large relative to your bankroll, you go broke before variance has a chance to even out.
The math of risk of ruin
"Risk of ruin" is the probability you go broke before you stop playing. The formula has three inputs: house edge, bet size relative to bankroll, and number of hands.
The relationship is non-linear. Cutting bet size from $25 to $5 cuts risk of ruin from 73% to 8%. Cutting it again to $2 cuts it to 2%.
The 5% session / 1% bet rule
The simplest framework that works:
- 5% per session. Take your trip bankroll and divide by the number of sessions. If you have $1,000 for a 3-day trip with 4 sessions/day, that's $1,000 / 12 = ~$80 per session.
- 1% per bet. Within a session, no single bet exceeds 1% of session bankroll. So $80 ÷ 100 = $0.80 per bet — round to $1 or $2.
This is far smaller than most players bet. That's the point. Most players go broke because they bet 5-10% per hand and hit a normal-variance losing streak.
Why session sizing matters more than skill
A perfect blackjack player with 0.5% house edge betting 10% of session bankroll per hand will go broke 35% of the time. A mediocre blackjack player with 1.5% house edge betting 1% per hand will go broke 4% of the time.
Bet sizing dominates skill. A bad player with discipline outlasts a great player with no discipline.
What this looks like in practice
A casual player who flies to Vegas with $1,000 and wants to "play blackjack and have fun":
Bad approach: Walk to a $25 minimum table, sit down, bet $25/hand. Expected to bust within 90 minutes per session. Good approach: Play $5 minimums for the first hour to learn the room and the dealer. Move up to $10 only after you've doubled the session bankroll. Take 5-minute breaks every 30 minutes. Stop the session when you've lost half the session allocation, regardless of how you "feel about" the deck.The advanced version: Kelly criterion
For positive-EV games (counted blackjack, video poker with progressive jackpots, certain promotional offers), the Kelly criterion gives a more precise bet size. Kelly says you should bet a fraction of bankroll equal to (edge / odds).
For most casino games, edge is negative — Kelly says bet zero. The 5% / 1% rule is a sensible heuristic for negative-EV games where you've decided to play anyway for entertainment value.
The whole point
Casinos make money because most players overbet relative to their bankroll. They go broke before variance has a chance to even out. The 5% / 1% rule isn't about winning — it's about lasting long enough that the entertainment value of a 4-day trip survives the first night.
For our hands-on take on which casinos have the lowest minimums (so the rule is easier to follow): see our directory.
Topics
- bankroll
- strategy
- discipline