No-Vig Fair Odds

What is the vig?

The vig(short for vigorish, also called the juice, margin, or overround) is the cut a bookmaker builds into their odds. It’s why the prices on both sides of a market add up to morethan 100% of probability — the extra is the book’s edge.

Why posted odds aren’t the real odds

Imagine a fair coin flip. The true price for each side is 2.00 (a 50% chance). A bookmaker won’t offer 2.00 / 2.00 — they’ll post something like 1.90 / 1.90. Those two prices imply 52.6% + 52.6% = 105.3%. That extra 5.3% is the margin, and it’s the reason a coin-flip bettor loses money over time even though the coin is fair.

How removing it reveals an edge

Devigging re-normalises those inflated probabilities back to 100% so you can see the fair odds — your best estimate of the true price:

• Implied probability = 1 ÷ decimal odds for each side.
• Overround = sum of both implied probabilities.
• Fair probability = implied ÷ overround, which forces the two sides to add back up to exactly 100%.
• Fair odds = 1 ÷ fair probability.

Once you know the fair price, you can shop around: if another book is offering longer odds than the fair number, that bet is positive expected value. This is the engine behind most +EV betting.

How Winora helps

Winora devigs sharp, low-margin markets automatically and compares them against every other Australian book in real time — posting the +EV gaps straight to your Discord so you don’t have to do the arithmetic by hand.