Combine 2-8 legs to see the combined odds and implied probability. Add your own estimated win % per leg to get the fair combined probability, break-even price and expected value.
Enter an estimated win % for every leg to see fair probability, EV and break-even.
Assume every leg's book bakes in the same margin. Margins don't add up across legs — they compound multiplicatively, which is why parlays are one of the most profitable products for a book.
At a 5% margin per leg, a 2-leg parlay compounds to roughly 10.3% total overround.
A parlay (or accumulator/combo bet) links several individual bets — "legs" — into a single wager that only pays out if EVERY leg wins. The combined decimal odds are simply the product of each leg's decimal odds: two legs at 1.91 each pay 1.91 × 1.91 ≈ 3.65 for a single stake, not 1.91 + 1.91.
That multiplication is also why the book's margin compounds rather than adding up. If a single bet already carries a ~5% house margin, a 4-leg parlay of bets at that same margin doesn't carry "4 × 5% = 20%" — it carries (1.05)⁴ − 1 ≈ 21.6%, because the tiny overround on each leg gets multiplied into every other leg's overround too. This is a core reason parlays are one of the most profitable products a sportsbook sells: the same per-leg margin becomes a much bigger edge once it's stacked.
Your implied probability from the combined odds is just 1 ÷ combined odds. If you also supply your own estimated true win probability for every leg, the calculator multiplies those together for a fair combined probability, and compares it to the combined odds to estimate expected value.
A parlay (also called an accumulator or combo bet) combines two or more individual bets into a single wager. It only pays out if every single leg wins — if even one leg loses, the entire parlay loses, but the payout odds are much higher than any single leg alone.
Combined decimal odds are the product of every leg's decimal odds, not the sum. Two legs at 1.91 each combine to 1.91 × 1.91 ≈ 3.65, and adding a third leg at 2.00 makes it 1.91 × 1.91 × 2.00 ≈ 7.30. American odds should be converted to decimal first before multiplying.
Because a book's per-leg margin compounds multiplicatively across legs instead of adding up. A single bet with a 5% margin turns into roughly (1.05)⁴ − 1 ≈ 21.6% total overround across a 4-leg parlay — far more than 4 × 5%. That's why parlays are consistently one of the highest-margin products a sportsbook offers.
Only when the combined odds pay out MORE than your own fair (true) combined win probability implies — i.e. fair probability × combined odds > 1. Since you're multiplying several individually-vigged prices together, the compounding margin (see above) usually pushes the combined price below fair value, which is why parlays are hard to beat even when a couple of the individual legs look like genuine value on their own.