How parlay math works
Parlays multiply. Convert each leg to decimal odds, multiply them all together, and that product is the parlay's combined decimal price. Convert back to American to display.
For example, three -110 legs each have a decimal price of about 1.91. Multiply: 1.91 × 1.91 × 1.91 ≈ 6.97. Subtract 1 and multiply by 100: that's roughly +597 American. A $100 wager returns about $697 in profit if all three legs hit.
Why parlays are harder than they look
The combined probability is also the product of each leg's probability. Three coin-flip legs (50% each) imply 12.5% combined; the parlay would have to pay 8.0 decimal (+700 American) to be break-even at fair odds. Books typically pay less than that, and the gap between fair and offered is the book's edge.
Same-game parlays compound this. Books price the legs as correlated, which means same-game parlays usually pay less than the math would suggest if the legs were independent.
Using this calculator
Add a leg, choose the format (American or decimal), enter the price. Add more legs as needed. The combined odds and payout update in real time. Adjust the stake to see scaled payouts. The math is exact and runs entirely in your browser.
For more on multi-leg pricing, see our Futures and Outright Odds guide and the American odds primer.