Calculating parlay odds takes three steps: convert each leg's American odds to decimal, multiply every decimal together, then translate back to American. That's it — no advanced math required, just careful arithmetic.
Why does the conversion math matter for parlay odds?
American odds (–300, +150, etc.) were designed for single bets, not multiplication. Decimal odds were designed exactly for chaining bets together, which is why every sportsbook's parlay engine converts to decimal under the hood before it shows you a combined line. Understanding the steps means you can verify any ticket before you place it — and catch pricing errors.
Step 1: Convert American odds to decimal
The formula depends on whether the line is negative or positive.
- Negative line: Decimal = (100 ÷ |American odds|) + 1
- Positive line: Decimal = (American odds ÷ 100) + 1
Applying that to the three-leg example from the Action Network — Packers –300, Patriots –200, Eagles –150:
| Leg | American Odds | Conversion Formula | Decimal Odds |
|---|---|---|---|
| Packers | –300 | (100 ÷ 300) + 1 | 1.333 |
| Patriots | –200 | (100 ÷ 200) + 1 | 1.500 |
| Eagles | –150 | (100 ÷ 150) + 1 | 1.667 |
Step 2: Multiply the decimals together
1.333 × 1.500 × 1.667 = approximately 3.333. That combined decimal is your parlay multiplier. On a $100 stake, the total return is $333.30 — meaning $233.30 in profit.
Step 3: Convert the multiplier back to American odds
When the combined decimal is above 2.00, use: American odds = (decimal – 1) × 100. Here that's (3.333 – 1) × 100 = +233, which matches the Action Network's published figure for this exact ticket.
How do parlay odds change as you add more legs?
Every additional leg multiplies the running decimal, which is why payouts grow fast. Three NBA game totals at –115, –110, and –110 combine to roughly +581 in American odds — a $100 bet returns $681.39 total. You can verify any combination instantly with the free parlay calculator on this site.
For a fully worked dollar-for-dollar walkthrough at the common –110 spread price, see the 3-Team Parlay Example: How a $100 Bet at -110 Returns ~$696. That page breaks down each multiplication line by line the same way I did above.
What the math reveals about the house edge
The vig baked into each –110 leg (roughly 4.5% per bet) compounds across every leg you add, pushing the average parlay house edge to approximately 24% — about five times what you'd face on a single-game wager. The Why Parlays Lose So Often: 24% Vig and the All-or-Nothing Rule page covers exactly why that compounding punishes bettors far more than most realize.
It's also worth comparing these combined odds against what you'd earn placing each bet separately. The Parlay vs Single Bet: Which Pays More and Which Costs You Less in Vig breakdown shows the tradeoff numerically. And if one leg ties, the parlay doesn't automatically win — the parlay push rules page explains how that reduces your ticket.
A note on Same Game Parlay odds
When all legs come from the same game, the multiplication above doesn't apply cleanly. Sportsbooks adjust SGP odds downward to account for statistical correlation between legs — a team covering the spread and their quarterback throwing three touchdowns are linked outcomes. Read more on the Same Game Parlay: How SGP Odds Are Adjusted for Correlated Legs page.
Parlay betting is only legal where your state has authorized sports wagering; check where parlay bets are legal in 2026 before depositing. Must be 21+ in most states. If gambling feels out of control, the National Council on Problem Gambling runs a free, confidential helpline at 1-800-MY-RESET, available 24/7.