Betting Mechanics for TTRPGs
Every once in a while your players will find themselves in a den of scum and villainy or even a more reputable horse racing hippodrome where they would be presented with an opportunity to improve their finances (or, very likely, lose their last pants) by betting on gladiatorial bouts, races and other sporting activities of good or ill repute.
1e DMG Appendix F (p. 215) lists a number of dice and card games, which to my liking are too convoluted for usage at the table, and Knave 2e (Downtime, p. 52) has a nice simplified system suitable for resolving a competitive one-on-one game, which is not suitable when trying to simulate a totalisator.
It should be noted that as a Referee you should avoid making betting a reliable source of income for the PCs - it is a game about adventure and exploring the world after all. Make up the limits on the maximum bet amounts, make sure that sudden wealth attracts unwanted attention, and other tricks in your Referee's repertoire. Remember, the house always wins!
With this said, here's a lean way of resolving the situations that I ended up introducing at my regular gaming group.
Betting on Results
The following rules apply for the situations when the player characters wish to partake in betting on fights, races or other competitive events.
Setting the odds: The Referee sets the odds in secret based on common sense, in-fiction lore, simulation or a random roll.
Investigating the odds: if the Players take reasonable actions that make sense in fiction to investigate the odds of the bet, the Referee may disclose the perceived chances of winning ±2 categories.
| Actual odds Decided by the Referee |
Chance of winning Roll d% for the actual result |
Monetary return on the bet Apply to the bet amount |
|---|---|---|
| Outrageously unlikely | 5% | 300% |
| Highly unlikely | 10% | 200% |
| Unlikely | 20% | 120% |
| Underdog | 30% | 80% |
| Somewhat weaker | 40% | 40% |
| Equal opponents | 50% | 30% |
| Somewhat stronger | 60% | 25% |
| Stronger | 70% | 20% |
| Likely to win | 80% | 15% |
| Sure win! Highly likely! | 90% | 10% |
| Win without question | 95% | 5% |
Example: the gladiatorial arena hosts a bout between a team of goblins and 2 hungry mountain lions. The goblins are seasoned arena veterans, who employ numerous tricks in their fights, and even though mountain lions are not pushovers, the Referee decides that the goblins are 60% likely to win (and, respectively, the mountain lions have 40% chance of winning). The Players decide to bet 80 gp on the Mountain lions. The referee either simulates the combat or rolls a die (for the lions it would be d% lower or equal to 40). If the goblins win, the Players lose their money. If the lions win, the players gain 40% extra on their bet for the total of 80 + 32 = 112 GP.