Understanding odds, probability and the vig

Two teams, a coin-flip game, and the bookmaker offers 1.90 on each side. Take either one at random, every week, and you lose money. Nothing about the teams explains that: the price does. Before any strategy makes sense, you need to read a price the way the market does.

Odds are probabilities in disguise

A decimal odd converts to an implied probability with one division:

implied probability = 1 / decimal odds

So 2.00 implies 50%, 4.00 implies 25%, 1.25 implies 80%. If you believe the true chance is higher than the implied probability, the bet has value.

The vig (margin)

Add up the implied probabilities of every outcome in a market and you get more than 100%. That extra is the bookmaker's margin: the vig (short for vigorish), also called the overround.

Back to that two-way market at 1.90 / 1.90:

1/1.90 + 1/1.90 = 0.526 + 0.526 = 1.052  →  5.2% vig

That 5.2% is baked into the price. It's the headwind every bettor fights: to break even you must win noticeably more often than the "fair" 50% those odds pretend to offer.

Why Pinnacle is the yardstick

Pinnacle runs on very low margins and high limits, and it welcomes sharp bettors instead of banning them. As a result, Pinnacle's prices are the market's best estimate of true probability. Strip the vig out of a Pinnacle line and you get the fair odds: the cleanest benchmark for judging whether any other price, or any strategy, offers value.

Removing the vig

To compare fairly, normalise the implied probabilities so they sum to 100%:

fair probability = (1 / your odds) / (sum of 1/odds for all outcomes)

This "no-vig" probability is what Bet2Invest compares against when certifying a pick. If your strategy's price beats the no-vig Pinnacle line consistently, you've found something real, which is the whole point of value betting.