Odds & lines for beginners

What are sports betting odds?

Sports betting odds measure how much a sports bettor can win vs. how much is wagered on a fixed-odds sporting event.

The different kinds of odds

There are three betting odds for Illinois sports bettors to consider: Fractional, Decimal, and Moneyline.

These are three terms saying the same things with different methods to reach the same conclusion. A closer look at each style of odds will demonstrate how these three say the same things with different processes:

Fractional odds

Fractional or British Odds are written with a slash (/) or hyphen (-) and are most commonly used by British and Irish oddsmakers. A fraction of 4/1 means the bookie will pay $4 for every $1 wagered. A 4/1 wager would return $400 for a $100 bet plus the original $100 stake.

If the 2024 World Series Future board or sheet looks like this;

A $100 wager on the White Sox would pay out $13 for every $5 wagered, and if the White Sox did indeed win, the wager would pay out $260 + the $100 stake for $360 (100 x 13/5).

A $100 wager on the Cubs at 9/2 would pay $9 for every $2 bet, and if the Cubs win the World Series, the punter will get $450 + the $100 bet for $550 ($100 x 9/2).

The best value or return on investment would be on the Cardinals. A $100 wager would return the gambler $800 plus the original $100 investment. The bettor makes the same $100 wager, but his return is higher than the others making his bet more valuable than the others.

Decimal odds

Decimal or European Odds are commonly found in Europe, Australia, New Zealand, and Canada. Favorites and underdogs are much easier to identify than Fractional odds simply by looking at the numbers on the board or sheet.

The decimal odds number represents the number one wins by wagering $100. This number represents the total payout with the original baked into the odds on the board.

If the 2024 World Series Future board or sheet looks like this;

A $100 wager on the White Sox would net the better $500 for a $100 bet (100 x 5.0). A $100 chance on the Cubs would earn $920 (100 x 9.2), and the Cardinals would gain the bettor $810 for every $100 wagered.

Moneyline odds

Moneyline or American odds are prevalent only in the US, where the favorite is denoted by a minus (-) sign, and the underdog is a plus (+) sign. Both symbols indicate how much one can win per $100 wagered.

The Illinois mobile betting app has listed the White Sox as World Series favorites, and a $500 stake is required to win $100. A $100 wager on the Cubs would gain $920 per $100 bet, and $100 wagered on the Cardinals is worth $810 plus the stake.

Why do betting odds on Illinois sportsbooks change?

Betting odds mainly change based on who is wagering on the contest. Still, they can also change because of a player injury, the weather forecast, or unknown circumstances before the opening line.

A line will mostly move because of a pro bettor, or sharp wagered money on a specific team. The result is the trader will then adjust the line toward the opposite direction of where the line was at the time of the bet. Let's use the Bears-Lions example.

Let's say the above numbers were on the board, and a pro better bet $10000 on the Bears -3.0. That bet would indicate to the trader that the -3.0 spread might be too low, and the bookie will either change the spread or the vig to remove the book's liability.

What has happened is the pro bettor moved not only the spread but also the price, and this is now an entirely different bet than the trader initially placed on the board. The implied probability has changed, as have the risk and payout.

How do I read odds?

To understand which bets are the best to make at the best odds, we’ll need to understand what components factor into the final number we see on the board or betting sheet.

Vigorish

Vigorish (“vig,” “juice”) is what the online sportsbook in Illinois charges you to make a wager.

If you bet $100 with your friend that the Bears would beat the Cleveland Browns and the Bears won, your friend would pay you $100, but sportsbooks don’t work like this. Instead, they attach an extra price or vig to the bet.

A $100 bet at -110 returns $90.91, and that missing $9.09 is what the bookmaker charges the bettor for making the wager. The “vig,” “juice,” or “tax” is how the bookmakers operate and how they remain in business.

Instead of wagering $100 on the Bears to win $100, the bettor would need to wager $110 to win $100. A winning bet would pay out $100 plus the stake or $210.

Conversely, a bettor placing a $100 wager on the underdog Browns winning this game would win $130, and the book would pay the punter $230.

Implied probability

Implied probability is the expected chance of an outcome as determined by oddsmakers or bookies, and it’s shown in fractional, decimal, or moneyline odds.

Professional sports bettors use implied probability to assess the value of a specific wager–the higher the odds, the more likely the bet will win. In contrast, lower odds decrease the probability of holding a winning ticket.

The White Sox at -500 has an 83.3% likelihood of winning–we arrive at that figure by dividing the stake ($500) by the total payout ($600), and we arrive at implied probability or likelihood the bet is going to win.

Conversely, a $100 wager on the +920 Cubs would land the bettor $1020, but the 9.8% chance of this hitting is why the payout is so high.

Negative Odds

Negative odds are represented by a minus sign (-) and inform the bettor how much they would need to wager to win $100. If a bettor wanted to win $500 at -110 odds, they would need to wager $550, and so on.

Chalk

Chalk is another term for favorite, and that number can be either a minus (-) or a plus (+). These are terms used by media talking heads and gamblers alike, and slang for “Favorite.”

Positive Odds

Positive odds mean the underdog, and that number is known by the plus sign (+), informing the bettor how much an Illinois sports bettor would need to wager to win $100. A bettor would stake $90.91 to win $100 at +110, and so on.

Pick-Em

A pick-em wager is a betting line without odds and pays the same price on both sides of the line. A standard moneyline pick-em wager would look like this;

A spread bet pick-em is listed as PK usually has a number next to it (+4.5) and would look like this on the board or sheet;

What a +3 spread is

Not all teams or players are created equal, and the oddsmakers attach a number based on how many points a team or player has to win or lose. A plus or minus odds spread bet can have three outcomes; it can be graded as a winner, a loss, and a tie or push.

A +3.0 wager means the Bears would have to lose the game by at least four points for this ticket to be graded a winner. If the Bears lose by three points, the bet is graded a tie or push, and the initial stake is returned.

What a -3.5 spread is

Sometimes the oddsmaker adds a decimal point or hook to a spread bet, and -3.5 means the favored team must win this game by four points for the betting ticket to be graded a winner. A stretch bet with a hook has only two outcomes and is either graded as a winner or a losing betting slip.

What a 20-1 bet is

A 20/1 bet is a long shot that is unlikely to happen and pays $20 for every $1 wagered. The odds are just 4.74% of winning, but an Illinois bettor wagering on a 20/1 longshot would win $20,000 if it lands.

Illinois-specific pricing checks that affect your bottom line

Because many Illinois bettors place lots of small wagers—especially live—pay attention to anything that changes your effective price. First, check whether your sportsbook adds a per-bet or “transaction” fee in Illinois; even a small fixed fee can erase edges on micro-stakes or low-hold markets.

Second, some promos (boosts, parlay insurance) meaningfully change the real price—recompute implied probability after a boost to see if value actually improved, and remember parlay boosts don’t offset the compounded vig from multiple legs.

Finally, line shop across several legal books: a 5–10 cents difference (e.g., -112 vs -105) swings break-even probability by multiple percentage points, which is often the difference between a profitable and unprofitable strategy over a season.

How to use betting odds to your advantage

While the odds are there to identify stakes and payouts, they can be used to an Illinois sports bettor's advantage:

Wager on -150 or lower moneyline favorites

Picking which team or player will win is challenging enough for anyone, but a beginning bettor should only play moneyline wagers of -150 and under. That would include underdogs of +150 and lower as well and offers the newbie the opportunity to get their feet wet without worrying about how many points a team must win by.

Sticking to the moneyline also allows the bettor to practice more advanced skills, like implementing implied probability in a less stressful betting situation.

Use multiple Illinois sportsbooks

The vigorish is how the books stay in business, but not all odds have the same juice attached, and why you want to have multiple accounts at different Illinois sportsbooks to get the best price.

Professional gamblers refer to the use of multiple sportsbooks as price or point shopping. What the pros do is have as many accounts or outs at as many sportsbooks as possible. Let's look at a pair of examples.

Sportsbook A

Sportsbook B

Both books have the same spread, but if someone were to bet on the Bears covering the -3.0, they would be better off betting on the Bears at Sportsbook B as the juice is .03 less than Sportsbook A. Conversely, sportsbook B offers a better price for taking the Lions for .02 more.

Those pennies saved don’t seem like much but do add up over the long term. That’s why it's essential to have as many accounts or outs as possible to find the best odds at the best price.

Bet on Underdogs

The vig keeps bettors from cleaning out the book, but a bettor needs to win 52.4% of their bets just to break even, and as we’ve seen, no two odds are the same, and it only makes sense to bet on a fair share of underdogs.

A general rule of thumb is to look for home underdogs with an implied probability of 42% (+135) or better, and if the bet makes sense, then make it but only if the risk makes sense. Don’t bet an underdog just to bet one; over time, you’ll begin to recognize when and when not to play a plus-money wager.