Kelly Criterion Bet Sizer

Calculate optimal bet sizes using Kelly Criterion. Supports single bets, fractional Kelly (quarter/half/three-quarter), multi-bet portfolio sizing, and max-bet enforcement. Use when asked about bet sizing, how much to bet, position sizing, Kelly Criterion, or bankroll allocation.

Calculate mathematically optimal bet sizes based on your edge and bankroll.

When to Use

Use this skill when the user asks about:

• How much to bet on a specific wager
• Kelly Criterion or optimal bet sizing
• Position sizing for a bet with known edge
• Fractional Kelly or conservative bet sizing
• Sizing multiple simultaneous bets
• Maximum bet limits or bankroll allocation

Odds Conversion Reference

Before computing Kelly, convert all odds to decimal probability format:

Format	Example	To Decimal Odds	To Implied Prob
American (+)	+150	1 + odds/100 = 2.50	100/(odds+100)
American (-)	-200	1 + 100/	odds
Decimal	2.50	Already decimal	1/decimal
Probability	40%	1/prob	Already prob

Operations

1. Single Bet — Full Kelly

Calculate the optimal Kelly stake for a single bet. User must provide: bankroll, odds (any format), and their estimated true probability.

bash

python3 -c "
import sys
bankroll = float(sys.argv[1])
odds_input = sys.argv[2]
true_prob = float(sys.argv[3])

# Convert odds to decimal
if odds_input.startswith('+'):
    decimal_odds = 1 + int(odds_input[1:]) / 100
elif odds_input.startswith('-'):
    decimal_odds = 1 + 100 / abs(int(odds_input[1:]))
else:
    decimal_odds = float(odds_input)

b = decimal_odds - 1  # net odds
p = true_prob
q = 1 - p

# Kelly fraction
kelly_f = (b * p - q) / b if b > 0 else 0
kelly_f = max(kelly_f, 0)  # never negative

implied_prob = 1 / decimal_odds
edge = true_prob - implied_prob

print(f'Odds: {odds_input} (decimal: {decimal_odds:.4f})')
print(f'Implied prob: {implied_prob:.2%} | Your estimate: {true_prob:.2%} | Edge: {edge:.2%}')
print(f'Kelly fraction: {kelly_f:.4f} ({kelly_f:.2%} of bankroll)')
print(f'Recommended stake: \${kelly_f * bankroll:.2f} of \${bankroll:.2f} bankroll')
if kelly_f <= 0:
    print('⚠️  No edge detected — Kelly says do not bet')
elif kelly_f > 0.10:
    print('⚠️  Kelly > 10% — consider fractional Kelly to reduce variance')
" BANKROLL ODDS TRUE_PROB

## About

Built by [AgentBets](https://agentbets.ai) — full tutorial at [agentbets.ai/guides/openclaw-kelly-sizer-skill/](https://agentbets.ai/guides/openclaw-kelly-sizer-skill/).

Part of the [OpenClaw Skills series](https://agentbets.ai/guides/#openclaw-skills) for the [Agent Betting Stack](https://agentbets.ai/guides/agent-betting-stack/).