Betting against the spread is the most common way to bet on NFL games, and it is also the one that confuses beginners the most. The idea is simple once you see it in action. Instead of betting on which team wins the game, you bet on whether a team beats the handicap the sportsbook has set. That handicap is called the spread, and it exists to make a mismatched game interesting to bet on. Without a spread, almost nobody would bet on a heavy underdog, and the sportsbook would have no balanced action on the game.

Here is a simple example. If the Chiefs are listed at minus seven against the Raiders, the Chiefs are the favourite and the Raiders are the underdog. A bet on the Chiefs only wins if they win by more than seven points. A bet on the Raiders wins if they lose by fewer than seven points, or if they win the game outright. If the Chiefs win by exactly seven points, the bet is a push, and your stake is returned. Many sportsbooks use half points, such as minus seven and a half, to remove the possibility of a push, so every bet has a winner and a loser. The minus sign always marks the favourite, and the plus sign always marks the underdog.

The odds on a standard spread bet are usually minus 110, which means you risk 110 to win 100. That extra ten is the sportsbook's commission, known as the vig or juice, and it is why you need to win about 52.4 percent of your spread bets just to break even. That number is important, because it means picking winners is not enough. You need to find spreads that are wrong, and you need to do it consistently enough to beat the commission. Most recreational bettors lose money on spreads not because they pick bad teams, but because they pay the vig on too many bets at bad numbers.

Key numbers matter more in the NFL than in any other sport, because of how scoring works. A touchdown with an extra point is worth seven, and a field goal is worth three, so the most common final margins in NFL games are three and seven. That is why the difference between a spread of minus two and a half and minus three and a half is enormous. At minus two and a half, a three-point win covers your bet. At minus three and a half, the same three-point win loses it. The half point around a key number is the most valuable half point in sports betting, and books charge a premium for it, so think carefully before you buy points across three or seven.

Finding value starts with making your own number. Before you look at the spread, form an opinion about how many points each team should be favoured by, based on their offence, defence, injuries, rest, travel, and motivation. If your number is three and the market says six, you may have value on the underdog. If your number is ten and the market says seven, you may have value on the favourite. If your number matches the market, there is no bet, and passing is the correct play. The best spread bettors pass on far more games than they bet on.

Spread betting rewards discipline more than excitement. Bet the same amount on each game, keep a simple record of your bets and the lines you took, and shop around for the best spread before you place a bet, because a half point here and there adds up over a season. Remember that the goal is not to pick the winner of the game. The goal is to find a spread that is wrong, and to bet it at a good price, with a stake you can afford to lose. Bet responsibly, set a budget, and never chase a loss by doubling your next stake.