How Parlay Math Works
A parlay is a single bet that links together two or more individual wagers for a high payout. To win the bet, every single leg must win.
Let's look at the math of a standard 2-team parlay where both teams are -110 (52.38% implied probability + vig):
- Leg 1 Win Probability: 50% (assuming fair coin flip for example)
- Leg 2 Win Probability: 50%
- Total Win Probability: 0.50 * 0.50 = 0.25 (25%)
However, the sportsbook doesn't pay you the "fair" odds. They bake their fee (juice) into the line, compounding their advantage with every leg you add.
Why Pros Avoid Huge Parlays
1 Leg
50% Win
2 Legs
25% Win
3 Legs
12.5% Win
4 Legs
6.25% Win
When is a Parlay Smart?
The only professional justification for a parlay is Correlation. This happens when one event occurring makes the second event significantly more likely to happen.
Example: If Patrick Mahomes throws for 300+ yards, it is highly likely that Travis Kelce also has high receiving yards. Betting these together in a Same Game Parlay (SGP) makes sense because the outcomes are linked.
Key Takeaways
- Keep parlays small (2-3 legs maximum).
- Avoid "Lottery Tickets" (10+ legs) unless you are okay with losing 99.9% of the time.
- Look for correlation where one win helps the other.