Implied probability is the win chance built into a betting line. American odds of -150 imply 60 percent; +150 implies 40 percent. Because both sides of a market add up to more than 100 percent, the excess is the sportsbook's margin, the vig. Removing it gives the market's actual estimate of each team's chance, which is the number a bettor compares to their own estimate to decide whether a price is worth taking.
Updated Sept. 16, 2026.
Odds are prices, and prices are probabilities in disguise. A -200 favorite has to win two-thirds of the time for a bet on it to break even; a +300 underdog has to win a quarter of the time. That break-even rate is the implied probability. If you think the favorite wins more often than two-thirds, the price is good; if not, the bet is bad no matter who wins on Sunday.
The two sides of a market never sum to exactly 100 percent. A -110 / -110 spread implies 52.4 percent each, 104.8 percent in total; the 4.8 points are the book's margin. Dividing each side by the total strips the vig and leaves the fair probability, 50 percent each. Moneylines carry different margins on the favorite and the underdog, so the strip is done the same way.
Implied probability is how a spread becomes a moneyline and back. A 3-point favorite in the NFL wins about 59 percent of the time, so the fair moneyline is about -145. Knowing the conversion is what lets a bettor tell when one market is out of line with another.
A game is priced Ravens -180, Browns +155. The Ravens imply 64.3 percent and the Browns 39.2 percent, 103.5 percent together. Strip the 3.5 percent margin and the market says Ravens 62.1 percent, Browns 37.9. If your model says Browns 42 percent, +155 is a bet.
American odds: negative odds of -X imply X / (X + 100); positive odds of +Y imply 100 / (Y + 100). Decimal odds of D imply 1 / D. Vig-free probability = a side's implied probability divided by the sum of all sides' implied probabilities.
For negative American odds, divide the number by itself plus 100: -150 is 150 / 250 = 60 percent. For positive odds, divide 100 by the number plus 100: +150 is 100 / 250 = 40 percent. For decimal odds, take 1 divided by the odds.
Vig is the margin built into the prices, visible as the two sides summing past 100 percent. To remove it, divide each side's implied probability by the total. On a standard -110 / -110 line, 52.4 percent each becomes 50 percent each after the strip.
About 59 percent for the favorite in the NFL, or roughly -145 on the moneyline. Key numbers matter: a 3-point favorite wins by exactly 3 in about 10 percent of games, so the conversion around 3 and 7 is steeper than elsewhere.
Category: Stats & Analytics. Part of the StickToTheModel NFL Encyclopedia.