Blackjack Risk of Ruin Calculator: Will Your Bankroll Survive?

Risk of Ruin (RoR) is the probability of losing your entire bankroll before achieving your profit goals. For card counters and serious players, understanding RoR is essential for proper bet sizing and bankroll management.

What Is Risk of Ruin?

Risk of Ruin calculates the probability of going broke given your edge, variance, bankroll, and betting strategy. Even with a positive edge, variance can deplete your bankroll before long-term profits materialize.

Quick Answer: RoR depends on bankroll/bet ratio and edge. With 1% edge and 100-unit bankroll betting 1 unit, RoR is ~37%. With 200 units, RoR drops to ~13%. With 400 units, RoR is ~2%. General rule: 200-400 betting units with 1-2% edge gives <5% RoR. Underbankrolled players with positive edge still face significant ruin risk.

How to Use Our Risk of Ruin Calculator

Use the Blackjack Risk of Ruin Calculator →

Enter your edge, bankroll, and bet sizing to calculate survival probability.

Step-by-Step Instructions

1. Enter Edge: Your advantage percentage

2. Enter Bankroll: Total playing capital

3. Enter Bet Size: Average or max bet

4. Input Variance: Standard deviation per hand

5. View RoR: Probability of going broke

Input Fields Explained

Field	Description	Example
Bankroll	Total capital	$10,000
Average Bet	Typical wager	$50
Edge	Player advantage	1.0%
Variance	SD per hand	1.15
Risk of Ruin	Bust probability	13.5%
Units	Bankroll/bet	200

Risk of Ruin Formula

Basic RoR Calculation

RoR = ((1 - Edge) / (1 + Edge))^(Bankroll/Unit)

Simplified for small edges:
RoR ≈ e^(-2 × Edge × Units)

Example:
Edge = 1%, Units = 200
RoR ≈ e^(-2 × 0.01 × 200) = e^(-4) = 1.8%

With Variance Adjustment

RoR = e^(-2 × Edge × Bankroll / Variance²)

Where Variance ≈ 1.15 for blackjack

RoR by Bankroll Size

At 1% Edge

Bankroll (Units)	Risk of Ruin
50	60.7%
100	36.8%
150	22.3%
200	13.5%
300	5.0%
400	1.8%
500	0.7%

At 1.5% Edge

Bankroll (Units)	Risk of Ruin
50	47.2%
100	22.3%
150	10.5%
200	5.0%
300	1.1%
400	0.2%

At 0.5% Edge

Bankroll (Units)	Risk of Ruin
100	60.7%
200	36.8%
300	22.3%
400	13.5%
600	5.0%
800	1.8%

Edge Sources in Blackjack

Card Counting Edge

Counting Skill	Typical Edge
Basic strategy only	-0.5%
Casual counter	0.5-0.8%
Skilled counter	1.0-1.5%
Team play	1.5-2.5%

Factors Affecting Edge

Factor	Impact
Penetration	+0.1-0.5% per deck
Rules (DAS, RSA)	+0.1-0.3%
Bet spread	+0.2-0.5%
Table conditions	Variable

Bet Sizing Strategies

Kelly Criterion

Optimal Bet = Edge / Variance² × Bankroll

Example:
Edge = 1%, Variance = 1.15
Kelly = 0.01 / 1.32 = 0.76% of bankroll

For $10,000 bankroll: $76 optimal bet

Fractional Kelly

Kelly Fraction	RoR	Growth Rate
Full Kelly	13.5%	Maximum
3/4 Kelly	5.3%	75% optimal
1/2 Kelly	1.8%	50% optimal
1/4 Kelly	0.1%	25% optimal

Conservative Approach

Risk Tolerance	Recommended Kelly
Aggressive	Full Kelly
Moderate	1/2 Kelly
Conservative	1/4 Kelly
Very safe	1/8 Kelly

Real-World Examples

Example 1: Recreational Counter

Profile:

• Bankroll: $5,000
• Edge: 0.75%
• Average bet: $25
• Units: 200

Calculation:

• RoR ≈ e^(-2 × 0.0075 × 200)
• RoR ≈ e^(-3) = 5%

Interpretation: 5% chance of going broke before profits materialize. Acceptable for recreational play.

Example 2: Serious Player

Profile:

• Bankroll: $25,000
• Edge: 1.2%
• Max bet: $200 (spread 1-8)
• Effective units: 312

Calculation:

• RoR ≈ e^(-2 × 0.012 × 312)
• RoR ≈ e^(-7.5) = 0.06%

Interpretation: Extremely low ruin risk. Can withstand significant downswings.

Example 3: Underbankrolled

Profile:

• Bankroll: $1,000
• Edge: 1.0%
• Bet: $25
• Units: 40

Calculation:

• RoR ≈ e^(-2 × 0.01 × 40)
• RoR ≈ e^(-0.8) = 45%

Interpretation: Nearly coin-flip on going broke. Need to reduce bet size or increase bankroll.

Downswing Probability

Expected Downswings

Downswing (Units)	Probability
25 units	~76% (will happen)
50 units	~37%
75 units	~13%
100 units	~5%
150 units	~0.7%

Downswing Duration

Losing Streak	Avg Duration (hands)
25 units	~1,000-2,000
50 units	~5,000-10,000
100 units	~20,000-50,000

Bet Spreading Impact

Spread Effect on Edge/RoR

Spread	Effective Edge	RoR (200 units)
1-4	0.7%	24%
1-8	1.0%	13.5%
1-12	1.2%	8%
1-16	1.4%	5%

Optimal Spreads

Penetration	Recommended Spread
50%	Not playable
67%	1-8
75%	1-10
83%	1-12

Common RoR Mistakes

1. Ignoring Variance

Mistake: "I have an edge, I can't lose" Problem: Short-term variance dominates Fix: Size bankroll for variance, not just edge

2. Overbetting

Mistake: Betting Kelly or more Problem: Maximizes growth but maximizes ruin risk Fix: Use 1/2 Kelly or less

3. Insufficient Bankroll

Mistake: Starting with 50-100 units Problem: 40-60% ruin probability Fix: 200-400 units minimum

4. Not Adjusting for Losing

Mistake: Same bet size during downswing Problem: Fewer units as bankroll drops Fix: Reduce bets proportionally

Frequently Asked Questions

What's an acceptable risk of ruin?

Professional players target 1-5% RoR. Recreational players might accept 10-15%. Above 25% is gambling on luck.

How many units do I need?

For 1% edge and <5% RoR: minimum 300 units. For <1% RoR: 500+ units.

Does counting guarantee profit?

No. Positive edge only guarantees profit over infinite hands. Short-term, variance can still cause ruin.

Should I use full Kelly betting?

Rarely. Full Kelly maximizes growth but gives ~13% RoR. Half Kelly is safer with 75% of the growth rate.

How do losing streaks affect RoR?

As bankroll drops, units decrease, raising RoR. Must reduce bet size proportionally.

What if my edge estimate is wrong?

If actual edge is lower than estimated, RoR increases significantly. Conservative estimates protect against this.

Advanced Concepts

Time to Goal vs RoR

Win Goal	RoR	Avg Time (hands)
Double (100%)	13.5%	50,000
+50%	8%	25,000
+25%	5%	12,500

Resizing Strategy

When bankroll changes:
New Bet = (Current Bankroll / Original Bankroll) × Original Bet

Down 25%: Bet 0.75× original
Up 50%: Bet 1.5× original (or lock profits)

Team Play RoR

Team Advantage	Description
Shared bankroll	Lower individual RoR
Larger spreads	Higher combined edge
Diversification	Variance reduction
Complexity	Coordination challenges

Pro Tips

• Start conservative: 1/2 Kelly or less initially

• Track results: Verify edge matches expectations

• Adjust dynamically: Resize bets with bankroll changes

• Separate bankrolls: Playing bankroll vs life funds

• Plan for worst case: Budget for 100+ unit downswing

Related Calculators

• Blackjack EV Calculator - Expected value
• Kelly Criterion Calculator - Optimal betting
• Blackjack Variance Calculator - Variance analysis
• Blackjack Card Counting Calculator - Count strategy
• Blackjack Session Bankroll Calculator - Session sizing

Conclusion

Risk of Ruin is the critical link between edge and survival. Our calculator shows that even with positive expectation, insufficient bankroll leads to high ruin probability. Target 200-400 units minimum with 1-2% edge for acceptable RoR. Bet fractional Kelly to balance growth and safety. Understanding RoR transforms gambling into calculated risk management.

Calculate Your Risk of Ruin Now →

A positive edge doesn't guarantee profit—it guarantees eventual profit if you survive. Proper bankroll management through RoR analysis ensures you'll be around long enough for the math to work in your favor. Size your bankroll for the worst-case scenario, not the expected outcome.